Lol, these are all awesome. My 2nd one:

I had my test-build fixed gear upside down in my living room and I was pushing the crank arms around with my finger to see if the chain was balanced. I was focusing too hard on the chain and stopped watching where my finger was. On the last pass my finger actually went into the chain's domain and my finger went halfway up the drive train with a chainring tooth going right through my finger nail. I couldn't just pull my finger "out" of it (it was totally stuck), so I had to actually backpedal a whole rotation to "eject" my finger.

Needless to say it hurt.