I would say that a fairly conventional list of the minimum requirements to be a man presented to boys would consist of the following:
Strength and Courage
Wit and Humour
Intelligence (Wit and humour serve to show some degree of intelligence)
A Competitive Edge. An ‘I will be the best at this thing’ attitude.
Masculinity is flexible, as long as the basic criteria are fulfilled a man can be good or he may be evil but he still is a man. These attributes may be found in many women too and the reason for this is that masculinity isn’t much of a way to differentiate men from women as much as to tell apart the men from the boys. In effect, this differentiation is not so different to the distinction between a child and an adult but the differences which warrant a gendered term are in the details.
At its most fundamental level, the differences stem from the generalised experience of male to female courting. Just as the male gaze brings out certain behaviours in women so do the generalised preferences of women, for lack of a better term, the female gaze, define and select for what the characteristics of masculinity are. Of course, men may then impose such characteristics on each other but the contribution of each gender to its formation is unquantifiable so I suppose it is safer to say that society as a whole is responsible for it.
The two most common criticisms levied against masculinity is that it promotes violence and aggressiveness towards others and that it causes repression of feelings in men. To the first two which are essentially one I have to say that in some instances violence and aggressiveness are in fact desirable and the capability for violence especially in men must not be demonized, in fact being incapable of violence is not a virtue in itself, having the capability to overpower others and yet also the restraint not to exercise it irresponsibly is a virtue, therefore the lower rate of violence in women is not necessarily a virtue either. The bottom line is that men are not broken women.
The repression caused by masculine ideals is a product of how men generally prefer to deal with problems in a practical manner, that is to say that men generally see no practical utility in sharing their feelings with others profusely, of course they are human and may speak to other men or to some of their friends usually while engaging in some sort of activity predominantly practiced by men, like I don’t know playing some violent video-games or whatnot but in any case an approach focusing more on the practical problems of men (like say unemployment) rather than their feelings is more likely to yield results. At any rate, it would work better to try nothing than trying to emasculate men for sharing or for not sharing what’s wrong with them, if they feel like it then they will share what they feel if not then let it be and seek another avenue to try to help them if that is what one really wants to do.
The one criticism I will accept about masculinity tentatively is that it stifles individuality to an extent by pushing an ideal onto him, by discouraging some behaviours and promoting others, but who finds every human behaviour to be acceptable? Well, anyone who doesn’t is in effect pushing an ideal onto others and stifling individuality.