@lillycoyote I think you were really on to something when you say it becomes apparent when they finally get some.
I have someone specific in mind, who I won’t name to cover my own ass, who was such an unpleasant, horrible, mean, BITCH for years. Until she met her (now) husband. The shift in her personality was instant. She’s a completely different person now. I think it is more than just sex that contributes to that crotchety mood, I’m sure a lack of intimacy in general would make anyone cranky.
The reason that I pinpointed this person in particular, is because there were other behaviors aside from the foul mood. Jealousy, and lashing out at people in happy relationships, going out of her way to draw attention to herself, etc. It was clear that she was lonely. The overall change in personality once she started getting some just sealed my opinion on the matter.