I get mad at smallest things too. Anger is not a bad thing, though. If you direct your anger towards something that you can't hurt, it won't hurt you or others.
Thing like screaming into your pillow, using a stress ball, a vigorous workout, or a good, long walk can all release the energy that is anger, and eventually help you figure out why you may get angry.
Never devalue that gave you some feeling, or set you into some mood. Everything you feel is valid to feel. If it didn't, you'd never have felt it. It's true that feelings can feel stupid, but they are your feelings, and that alone makes them important.