Hater

A 'hater' is literally a person who hates something, but it has taken on a more specific meaning. A 'hater' is a person who doesn't like you or holds a grudge against you. They doesn't necessarily want what you have, but they are jealous of your success and want to knock you down a few notches.

Examples:
-Justin Bieber sucks!
-Don't be a hater!

-People can be so judgmental.
-Yeah, there are a lot of haters.