I have recently come into contact with several quite funny men, due to something I've become involved with. (Something with which I've become involved, for you grammarians). One of these very funny men was previously involved with something similar, but all male.
Which, it seems to me, is not a departure from several highly influential funny things. Monty Python, for one. Are women not as funny as men? Or is it just that men dressed as women, or imitating women, are more funny than women as women could be?
It seems that if the man in a dress theory were correct, then successful comedic troupes performing sketch comedy and the like would be disproportionately male, while forms of comedy that don't involve characters would be entirely gender balanced, or at least nearly. Standup, which is verbal, and doesn't usually involve complete assumption of characters. So, we would expect to be able to list as many funny male stand ups as funny female stand ups.
Unfortunately, I'm hard pressed to list more than three funny female stand up comics. And one isn't really a stand up comic, being more of an actress who occasionally does stand up than a comedian. Sarah Silverman. Also funny and female is Maria Bamford. And there's this hungarian lesbian who seems to be fairly funny. But as I can't remember her name, it is very possible that she isn't successful. Sure, there are other female comics who are amusing or popular, but there men who are popular and not funny; See Jim Breuer.
So why aren't women funny?
A certain segment of feminists would explain that women ARE funny; that women do not actually make people laugh or become successful in professions that require humor can be explained by the male-dominated media culture. Because women are not funny like men, we do not believe that they are funny at all. These feminists would explain that female humor is inherently different than male humor, but just as valuable. They would explain that it is more gentle, narrative, less absurdist. And for these reasons, it does not get as much attention and praise as male humor.
Another segment of feminists would say that those feminists are being sexual determinists in believing that individuals are more defined by physical gender than by the choices they make and the culture they live in. These feminists would say that women are not funny because society pressures them to be quiet, demure, ladylike, and cede the spotlight to men. Society pressures women to be sexually appealling and attractive, qualities that may be risked by making faces and saying things like "ass-magnet". These feminists might insist that it is our culture that forces women to choose between being pretty and witty.
It may be a combination of both of these factors; some women are not funny because they are by nature unfunny, and some women are carefully nurtured to be not funny. And some are feminists who deliberately cultivate humorlessness.