Or, sometimes those bitches do it on purpose, because they're pissed at you for some stupid shit, or because they know they can. They enjoy watching you squirm, trying not to think about it.
Then you excuse yourself to the bathroom and try to rub one out, but you can't cum because you know that her pussy is so good that you just CAN'T go back to the old shit!
Meanwhile, your balls swell with sexual tension, aching every time you move, until finally you can't take it anymore. You have to give in to get some of that sweet, tight pussy!!
Dude 2: What's wrong?
Dude 1: My girlfriend went on a Pussy Strike, and I haven't came in four days!
Dude 2: Heh... Yeah... Just get a Fleshlight and keep it duct taped under the bathroom sink. I named mine Cristal.