The trick is to pretend that you hate everyone. Then it won't be out of character when you say you want to punch someone in the face.
Also, as an added bonus, people are always caught hilariously off guard when you say or do something nice.
Gahh, all this pretending stuff is so annoying. Can't we all just evolve into sea-urchins? Sea-urchins just lie in clumps on the ocean floor, they don't have to pretend to be anything. Plus the spines repel all the annoying creatures of the sea.