Scientists at the University of Toronto examined people's facial expressions after they tasted a bitter liquid, looked at pictures of dirty toilets, and found out they'd been cheated in a game. The reaction was always the same: A wrinkled nose and raised upper lip. Cavemen had the same response to poisonous food.

What does Cro-Magnon Man's bitter taste have to do with your bitter reactions to bad clients and colleagues? The common facial movement illustrates that people react to moral and physical disgust in similar ways. So shaking a dreaded pet owner's hand could cause the same physical feeling as drinking sour milk. Here's the positive side: Gargling a little mouthwash or chewing a piece of gum could give you a fresh outlook when you're feeling slighted.