Things that gross me out:

Chewing on a warm towel (which I don't think I've ever done, but good golly, just thinking about it is enough.)
Cracking knuckles.
White gunk on teeth.
Two paper-wrapped straws rubbing together (Oh My GOD - seriously - that makes me want to freak out.)
Loud chewing/teeth chomping/jaw popping.
Cans being crushed.
Pre-formed styrofoam being pulled out of boxes.
When one of my socks is on crooked under my shoe.