E.D.
I throw a tantrum.
Nope, not kidding.
When I'm starting to bug myself, I'll stomp around the house and make fun of my bad attitude, and then roll around on the floor like a dying fly, yelling "I'm so gruuuuuuuuuumpy, whine, whine, whine, POOOOR Ephie, poooor meeeeee". By then, I'm laughing too hard to be grumpy anymore.
That, or I sit outside by myself for a few minutes, take a shower, or get onto MP.