I stim when I'm anxious or happy. I have noticed, however, that I have more stims for being anxious and scared than I do for being happy.
My stims for when I'm anxious include:
- Biting/picking at my fingernails
- Pulling out my eyebrows and eyelash hairs, and bringing them to my lips to "feel them"
- Rocking back and forth slowly, then faster (not to be confused with my "happy" rocking stim that I will bring up in a moment)
- Singing to myself to block out auditory input
- Rocking back and forth on my feet
My happy stims are:
- "Happy" rocking, like when I'm watching funny videos on Youtube, or one of my favorite movies, such as Cars, Cars 2, Planes, Finding Nemo or Chicken Run
- Stroking or petting a stuffed animal
- Listening to music and dancing around my room while tossing a small piece of cloth thru the air
- Covering myself up with a blanket and wrapping it around myself like a Snuggie or a cocoon (and when I was a kid, I loved stimming the way the little boy does in the video LupaLuna posted.
)
I do try to control/redirect my anxious stims in public, such as by playing with stones or a Tangle toy rather than biting and picking at my fingernails. Sometimes I can't, tho, when I'm really stressed - last week I got really anxious in one of my classes, and I rocked a little bit at my desk. I don't think anyone noticed, tho. I stim without even thinking about it, most of the time...and it wasn't until I joined WP that I realized that some of the stuff I did that I thought no one else did was, indeed, stimming. 
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I wish Sterling Holloway narrated my life.
"IT'S NOT FAIR!" "Life isn't fair, Calvin." "I know, but why isn't it ever unfair in MY favor?" ~ from Calvin and Hobbes