Something got you down? Angry at someone? Don't sit and let the anger overtake you. Instead, use your emotions to fuel your workout.
I've found that if I decide that instead of getting mad I'll get even by getting thinner/hotter/more fabulous then I have a better, harder workout than normal. Instead of feeling guilty about comfort eating or being lazy or having excuses to not eat right or skipping the gym, I feel fantastic because of the workout.