Whenever I feel bad, 

I just shout 'Expecto Patronum'

then I feel okay

 -------------------------------------------------------------------------------------------------------------
Here's a trivia which I just learned from Wikipedia.
Suggested etymology: Expecto Patronum is correct classical Latin for "I await a protector". It is related to "pater" (father) and Harry's Patronus indeed takes the same form as that of his father's animagus form (a stag).