One of the earliest pornos I remember had this plot. It was super weird and freaked me out, which is why I remember it. It was a very old brazilian porno, which was basically just an actual movie (more than 2h long, only one or two sex scenes, even though they were hardcore scenes showing everything with a couple of boobs here and there).
There was this one guys who had a girlfriend and two of his friends in his house and all of them were horny. The girlfriend came and the couple moved it up to the bedroom, where the two friends were hiding in the closet. The guy with the girlfriend convinced her to put a blindfold on, saying it was fun and kinky. Then, the two friends quietly came out and the 3 of them started taking turns, sometimes playing with her boobs while someone else fucked her and that kind of stuff. Eventually, they started having more fun with it and at one point one guy stuck his dick in her mouth while she was getting fucked. That's when she freaked out and took her blindfold off and saw the three friends. But this was like a real movie, not a porn, so she obivously flipped her shit, I don't really remember exactly what, but I think she started screaming or maybe slapping them and one of the guys panicked and just smashed her head with a lamp or something. She just instantly died and the guys didn't know what to do. After a lot of panic and confusion, they ended up putting her body in the trunk of the boyfriend's car and driving off to get rid of it. I don't think I ever finished the movie, I was pretty young and was just looking for some porn at the time and was met with that shit that almost ruined my mood that night.