People will jump to any chance to ridicule others. Especially when it comes to pointing out a person's biggest insecurity. For guys that would be their size. Add in the fact that unlike girls, guys are told to just man up and deal with it so making jokes about them somehow becomes acceptable when if you were to do the same thing onto a woman you'd be considered heartless. 'Cuz guys don't have feelings n shit.
Some women are smug, judgmental cows. That's the way it is. I remember a bitch I had a one night stand with said something cheeky to me when I was leaving hers. Wasn't about my dick but I took umbrage with her. Called her jelly belly and she went nuts. Its easy to take the wind out of someones sails. Just find what they fear most then use it. The people hurling the insults are usually the ones with the most to hide
Because porn has taught men that young hot females drool and fawn over baseball bat sized dicks that stretch women wide and every man at some point in their lives will come across the "size queen" who will dump you cause your not packin a sub marine between their legs!