It's the porn ego version of: when an unstoppable force meets an immovable object -- where the guy knows he's got a huge cock and is trying to prove he's too big for her by making her tap-out, and the girl knows she's got a tight pussy that most guys can't take for long and she's trying to maintain a steady rhythm that will make him have to pull-out -- and their egos make them play a game of chicken.

There's actually two variations on this -- one is if the pros are acting-out a plot where their characters are supposed to be that way, and the other is the performers have real egos that are butting heads.

One example is Avy Scott vs. Mandingo -- he kept pulling out and she seemed to enjoy taunting him to put it back in, going so far as to ask repeatedly, "are you running from me?"

Another example is Gina Lynn vs. Lex Steele -- she seemed to be trying to prove she could get him to cum early (as he was known to do) but her pussy just couldn't take it, so she had to keep pushing him off her, but then would immediately go back to trying to show she could take everything his cock could dish out.