Another one of mine is people who are in some sort of competition that you never knew about. As in, you spent 5 minutes talking to her, but only 3 to me. You spoke to her about XYZ, but not to me. You held her baby at the party, but not mine. Makes me want to tear my hair out, all the while wondering what happened to this person in their childhood to make them so incredibly insecure.
^UGH........can't believe I forgot about that one. It's so annoying. Some are not even that discreet about it. The kind that will say, "So you're trying to outdo me there?" And you're like "Huh? What? Come again? I wasn't aware there was a competition."