stealth hater
A stealth hater is someone who doesn't have the courage or intestinal fortitude to confront you or express their hate for you to your face. They will tell everyone else why they hate you. They will either pretend to like you to your face or not say anything at all. The worst kind of hater.
Anna is such a stealth hater - she won't serve me or talk to me at the coffee shop unless she has to - and puts on the fakest smile and attitude one ever did see.