I like to think I'm a nice person. When I have food, I offer it around. Say I've got a bag of crisps at the office. Everyone takes a couple, UNTIL you get to the one person who takes a huge handful. Ok fine you always bloody do that but whatever
but NOT ONLY THAT, for the rest of the bag's short life will treat MY crisps like a shared bag and take handful after handful until they're all gone. 😡
WIBU to bite her next time?
Caveat: she's a lovely person just a greedy git 
Lighthearted of course, but the biting may be genuine if she does it when I'm PMSing.