I can't stand:
Shallowness
Materialism
Vanity (esp. people who worry too much about their image and appearance, and subsequently have no character or personality)
Dishonesty
Insincerity (in giving compliments, acting all friendly and nice to everyone)
Selfishness
Lack of respect for others
Tactlessness
People who think they know everything and love correcting everyone
People who love the sound of their own voice and talk too much nonsense
People who lose their temper when they don't get their way all the time
People who try too hard to please people and have no opinions or identity of their own
People who write up big lists of things they don't like about other people when they're far from perfect themselves :embarasse