Yeah, I considered putting it in my post but ultimately cut it, but it is indeed often romantic couples who have this problem. Not always, but often it's couples. I think good-natured competition is typically a part of an ordinary friendship, even a very close one (Impro's take on status-games, and friendship being largely defined as a relationship in which you can play such games safely and without "real" stakes, probably factors into this) is probably why this happens less often with friends. Though, certain friend pairs, if you get them together in a group of people they don't know, they'll do this too.