>>9235
Good points! There is also the classic oral sex in the back seat of a car, then a sudden traffic accident causes her to bite off his penis. That seems like plenty of erotic context.

Another idea would be swimming naked in the wilderness and having sex when some sort of animal attacks, like alligators, piranha, or even candiru.

>>9227
Fantasy play turning bad is quite interesting. For example, a couple might enjoy knife play with their sex, until the boy accidentally really stabs his girlfriend in her pussy. In the resulting pain and rage, she might chop off his penis or do all sorts of horrible things.

Or the roles might be reversed with her accidentally cutting off his penis and him taking revenge. It's hard to decide which would be better.