People laugh when they hear a "sexist" joke because it's funny. Maybe gender related jokes don't have a place at conferences and work places - I am not sure - but there should be room for jokes about genders somewhere, right? I mean, where does this political correctness stop?
The simple fact is that "jokes" which reinforce current power structure are not good jokes. As a man you don't get to decide how women should feel about scantily clad ladies in technical talk slides, just as a white person you don't get to tell black people how they should feel about affirmative action. When you make philosophical proclamations about the world from a position of power you're no different from a jock making fun of a nerd because "he looks funny".
Just a modicum of empathy is all that people want in the vast majority of cases.