A page on the Geek Feminism Wiki defines a grunch as one of those little moments that just causes all of your illusions of being seen as an equal to fall apart.
From an outstanding article by Tim Chevalier about programming, women and sexism, entitled How To Exclude Women Without Really Trying. Read it!
Here is just a taste:
Countering sexism requires courage and (in Samuel Delany’s words) moral stamina. It is work that largely needs to be done by men, since men who tacitly believe that women aren’t quite human are hardly going to listen to women’s opinions on the subject.