This is going to sound rather petty and whiny, and indeed it is a pretty small annoyance in the scheme of things, but nonetheless:
Fake gift-giving. That is, the practice of buying someone a "present" with yourself in mind, then
immediately asking for a long-term loan of said present. Really, who do they think they're kidding?
(Yes, yes, this just happened to me, of course– can't you tell?)