H.W.
I have different mantras for different times.
PMS-ing: "It's not them, it's me. It's not them, it's me." Keeping reality in perspective at a time when my perspective is shot.
Visiting my crazy family: "It's not me, it's them. It has *nothing to do with me*."
Most other grumbly times: "Be happy to have what you have to be happy with." (It's a King Crimson song, but ever-appropriate)
Today is mantra-free. I'm getting to meet a girlfriend for a beer later this afternoon. :)