Casual misandry is a phenomenon where unfounded negative claims are made about men as a group, or men as a group are insulted or put down. Both men and women can engage in this behaviour. It is much more broad than male bashing which is usually more direct in its attacks on men. Casual misandry often consists of over-simplification, half truths or in some cases outright lies. Casual misandry may be a recent learnt behaviour. It has certainly become more prevalent in recent decades.
Selected examples of casual misandry are presented here.
Men are genetically inferior
These claims usually come about as suggesting that the Y chromosome is somehow defective and is ultimately doomed. These claim can occur because the Y chromosome is smaller than the X chromosome, contains fewer genes, and may once have been an X chromosome that lost a leg. These sorts of simplistic claims show a fundamental misunderstanding of genetics. There is no clear relationship between number of genes and complexity in multi-celullar organisms. Research shows, for example, that humans have less genes than grapes.
Every difference between men and women comes, directly or indirectly, from the Y chromosome. To claim that the Y chromosome is a disadvantage for men is to reject everything it is to be male and to reject all of the achievements of men, now and in the past.
Men have lower pain thresholds than women
On the surface this may seem to be logical. Women experience childbirth so it seems reasonable that they would have higher pain thresholds. Surprisingly, no one had scientifically tested this assumption until recently. Scientists actually discovered that men tend to average significantly higher pain thresholds. This means that a man would experience less pain, on average, than a woman would in a comparable situation. Very recent research has found that men may experience more pain than women after major surgery but that the reverse is true after minor surgery. Scientists found that pregnant women do tend to have very high pain thresholds although this is lost soon after birth. Male animals injected with female sex hormones experienced a reduction in pain tolerance.
Differing gender experiences of pain have implications for pain management so it is important that the medical profession recognise that women often experience more pain than men and apply this knowledge appropriately.
Men and boys are stupid
Boys are stupid, throw rocks at them is a line of products produced by the corporation David and Goliath. This product line held to the notion that boys are stupid and endorsed violence against them. The products continue to be available for purchase. This clothing line is just a particularly egregious example of a widespread trend. While this may be intended to be humourous, humour does not excuse prejudice.
As is widely recognised today, men are routinely portrayed as stupid in popular culture.
In 2012 it was widely reported that women had passed men in IQ These claims came from statements made by a well known intelligence researcher from New Zealand, James Flynn. Flynn states unequivocally that he was misquoted and that he was reporting that women had caught up to men in IQ.
Men are linear thinkers
Another widespread but baseless claim often made today is that men are linear thinkers while women are not. Variations on this idea include that men are more rigid thinkers, that women are more capable of thinking outside of the box or that the male brain is more specialised.
These claims include the notion that men are unable to alter their thought processes to match a changing situation and are less able to think of novel solutions to problems.
These claims tend to ignore the fact that men are responsible for the overwhelming majority of innovation, invention and problem solving, today and throughout history and form the vast majority of people who work in unstructured work environents (eg, police) or who solve problems for a living (eg, engineers). Women tend to choose occupations where the tasks are more structured and clearly defined (as well as generally being cleaner and safer).
Claims relating to women thinking outside of the box are in fact nonsensical. One can only think outside of the box relative to those thinking inside of the box. As such, if we consider that men and women in general think differently then each group will tend to think outside of the box relative to the other. This is in fact a corollary to the notion that diversity in opinions on solving a problem can lead to better outcomes.
Claims about male thinking usually go on to claim that women will lead in the 21st century and that this is reflected in increasing female participation in the labour force. Interestingly while female labour participation rates increased from the 1970s they peaked around 2000 and have been steadily declining since that time 
Men can't multitask but women can
It is actually true that men can't multitask, but neither can women. The overwhelming evidence suggests that anyone who thinks they can multitask is deluding themselves and that people who try suffer a net loss in productivity.     Attempts to multitask may even increase stress levels and ultimately impact health in a negative way. Humans are capable of continuous partial attention which allows then to perform multiple activities at once but in general these must be simple activities and there is still a net loss of productivity.
Men can't maintain attentiveness as well as women
A recent article in The Times of Israel highlights this belief:
Speaking in her officer’s presence, she never once swiveled her head or removed her eyes from the screen. “Their powers of concentration are incredible,” the intelligence officer said, noting that very few males would be capable of maintaining the grueling attentiveness necessary to patrol a stretch of road for four straight hours.
In actuality men have routinely maintained vigilance for long periods of time during conflicts (and for other reasons) throughout history. Software Developers (85% men) routinely stare at screens without interruption for periods that are often much longer than four hours.
Men think about sex every few seconds
This claim varies in frequency and is of uncertain origin. Some reports state that men think about sex as often as every seven seconds. This claim has been throughly debunked and is without merit.
Men have fragile egos
The claim is made that men are so emotionally fragile that opening the door for them damages their self-esteem and self-confidence. The news site The Wire tells us that Men Are Fragile and Do Not Need Your Common Courtesies, Says Science.
The online dating site Lavalife feels that women may need to take men down a peg or two to keep their egos in check but goes on to say:
Guys pretend to be tough, impervious to pain, but the ironic thing is that the male ego is as fragile as an egg. Or, as NewYorkMoments writes on the appropriately titled blog Tired of Men, “The male ego is like a zeppelin. It’s big & bloated & full of hot air. In fact, it’s so big it floats, but one little spark destroys the entire thing.”
Men complain unduly when sick (Manflu)
Today many people apparently believe that when ill with a minor virus men complain more and remain sick for longer. This is commonly known as manflu. Some companies even feel it is acceptable to refer to a man as a man-child while sick.
manflu.info tells us:
Man Flu is a crippling and debilitating disorder indiscriminately striking down male members of the human species without warning. The illness is often referred to pejoratively by female members of the species who are in fact immune from the illness as man flu is now known to exclusively attack the XY chromosome carrier. If Man Flu is kind enough not to kill the infected party it will definitely leave him weak, sick, hurting everywhere and in dire need of TLC.
While this site is obviously intended as satire the sad truth is that a lot of people, especially women, believe this to be true despite solid evidence to the contrary.
What’s that? That sounds a lot like regular flu you say? Well spotted and correct! Man flu presents exactly the same as it does with regular flu except for an added degree of difficulty commonly known as “chronic exaggeration”. In fact, Man Flu, according to absolutely no credible source whatsoever is:
13 times worse than normal flu
More unbearable than childbirth
Easily recognisable when the patient continues to tell you he really wants to go into work but is too selfless to risk spreading his awful condition amongst his work colleagues.
Only cured by moaning. A lot of moaning.
In reality, while the exact rates vary from country to country, women take more sick leave from work than men.  While some may suspect that women are taking additional sick leave to care for children, childless women take more sick leave than childless men.  One study reported that women take 50-70% more sick leave than men performing the same work in Norway.
Men are immature, child-like and emotionally stunted
This criticism is often levelled at men who are choosing to remain single throughout their lives. The argument presumes that because these men are not following a traditional path of attempting to form a permanent relationship and choosing to have children that they are immature. This is an inherent value judgement. People who recognise that they do not want to be parents (or are not cut out to be parents) and make sure this doesn't happen may well be more mature and responsible than people who plunge in to relationships and parenthood without having considered the long term ramifications of these choices.
CNN, like others, argues that women are better at dealing with emotional problems than men. It would be more accurate to say that men and women tend to deal with emotional problems in different ways and claiming one method is better than the other is making a value judgement.
Statements like the one below, often couched in humour, suggest men are more simple than women:
Men have two emotions, hungry and horny. If you see him without an erection, make him a sandwich.
This is perhaps the most insulting and dehumanising of all of these claims.
Men don't ask for directions
It is often claimed that men do not ask for directions. Despite how widely repeated this claim is there is very little evidence to suggest it is actually true.
Men speaking condescendingly to women (Mansplaining)
Mansplaining is the notion that men routinely speak to women in a condescending manner and in particular do so far more often than they would do so to men. This term is now widely used by women. Stories of men engaging in this behaviour are widely available online.
One of the principal problems with the concept of mansplaining is that it presumes that the men talking in a condescending manner only do this to women. They may simply be arrogant individuals who act this way towards many people, regardless of gender. Because of the inherent assumption about the gender bias of someone who is allegedly mansplaining, the concept is unflasifiable. It is not possible to prove that these men would never act that way towards other men.
Men aren't as efficient or effective workers
From time to time it is asserted that women are just better workers than men. For examples, this article in the Daily Mail:
Women DO work harder than men: How female employees are less prone to distraction and more likely to get a job done This alleged study monitored male and female employees for 10 minutes per person and failed to control for various factors, such as the men and women actually performing different jobs or even establishing what constituted work. Someone reading a technical article would appear to not be working in the above study.
In contrast at least some hard data suggests men are slightly more productive workers, at least in blue collar roles. In practice the difference is negligible in most positions. There is a notable exception however, in which female scientists had significantly lower scientific publication rates than male scientists.
Statements like these are common in western media. Many men and women believe these myths about men. It is reasonable to expect that constant denigration of men and masculinity will have a negative effect on men and boys. Of particular concern are boys being born in to a world where they are taught from a young age that there is something fundamentally wrong with being male. If we do not stop spreading these lies and half-truths about men and boys we will continue to see young men and boys disengaging from society in ever increasing numbers. If this trend continues we will all be the poorer for it.