grab a digital camera. go to somewhere quiet and take pictures of anything. then turn the camera on yourself. don't fake a smile. photograph your grumpiness.
keep taking pictures until something shifts. maybe its the sunshine, or that you feel beautiful or are wearing the most gigantic earrings. or maybe its just that your grumpiness wanted to be witnessed. smile, for reals.
be silly. laugh at your ridiculous bed-head or a trying to be cool-face that didn't fly. don't anyalze it. just play.
keep taking pictures. keep playing. smile (or don't). go home feeling like a different person.