Well this is a sensitive subject because different people are into different things. Usually I like to fist girls but not in the vagina but in the face. Ya get the joke? I hit girls. But only if they ask me to in a moment of passion. Or if like they make my bagel wrong. C'mon, PUMPERNICKEL?! FUCK THAT! Everything bagel or no the fuck thank you.

But in all seriousness you should do whatever you feel comfortable with, even if that means fist pumping your whore of a girlfriend's extremely wide-set vagina. If you won't, her boyfriend will.