I've had girl's bfs pick them up from my place (we'd walk a block or so first) after havign sex with them. I've slept with girls on their boyfriends' couch and made an awful mess in the process. Never knew the dudes.
I don't regret it but it ultimately isn't what you're probably going to be looking for if you have half a brain. I was young and stupid - still am for the most part but thankfully I'm growing out of treating people like shit. Bouncing wasn't helping at the time though.
Anyways, it's not a cool thing to do, that's for sure. But usually I've found good people who would never think of cheating don't get involved with sketchy people. I used to think like of it like if she's sleeping with me then even if someone THINKS she's his gf, she clearly is not.