trip'n fall

To have sex with someone even though you were planning not to or even though you know that it's a bad idea.

Girl: I always say I'm gonna wait, then I kiss a guy and I trip'n fall.

Girl: I saw my ex last night
Friend: And?
Girl: I know I said I was over him but I tripped'n fell. He's an asshole but he's still a good fuck.

Guy: I didn't mean to. I just kinda tripped'n fell.
Girl: And what? You just tripped and fell and your cock just magically landed her pussy?
Guy: Umm...