I absolutely can't stand:

Smacking/Chewing Loudly. Drives me absolutely insane.

Chair Bumbing- or someone bumping into the back of your chair. I had serious issues with this in the college cafeteria. I would purposely try and sit where it woudln't happen, but it still always did. There were several times I almost stood up and screamed at someone. I have no idea why it bothers me so much lol