You've seen this on the sitcoms, but I think it rings true.
You're in a relationship with someone, and they are really starting to piss you off. You get into a heated argument and you are feeling so many things, hate, anger, resentment, lust, respect, admiration for the other guy standing up for himself, etc. Neither of you have any idea what to do with all this pent up energy and emotions..and then someone will touch the other one...and that will be it....sex.
No one won the argument, and it definitely wasn't make up sex since there was no making up. I don't want to call it anger sex since it is not abusive in any way. I guess it is using the negative energy in a positive way.
Not as good as make-up sex...but yeah...it can be good.