Not exactly a co-worker, but one of the devs from the client's team spent a few months working in our office next to us. He would always take a nap at lunch time and snore loudly, and eat an apple afterwards and it seemed to be impossible for him to chew with his mouth closed.

Whenever he had a cold and his nose got blocked he would still force himself to breathe through his nose, so it sounded something like a mix of darth vader and someone drowning.

He also lacked any notion of personal space, and would always sneak behind us to ask questions and then put his laptop right on top of our keyboards or in front of our screens and start talking while we still had headphones on.