I think my biggest turn off is lip smacking. I can usually ignore it, but if you are a bloody pig that cannot go a moment without eating chips in front of the tele without keeping your stupid, filthy trap shut, I will lose it and leave the room.
This excludes when it is proper, such as slurping soup in Japan. I only speak of the gum-chewing, cheek sucking, wet cesspool of a face thing.
On an unrelated topic, the sound of a dog drinking water or repeatedly licking something is at the same level. There was once a dog licking a bone on the tele. That was the entire commercial. Nothing except a dog licking a bone. No music or dialogue. With amplified dog slurping sounds. For thirty seconds. It was so bad that I could not watch channels with it, as they would show the commercial at every break.
Up there on my 'biggest turn off' are:
Picking nose and eating it in public. If you are older than eight, this should have passed. If you are Thirty Eight and cannot get a girlfriend while digging for jewels in your snot-leaking facial holes, it's a wonder.
Sharp noises. Similar to lip smacking, except I am overly sensitive to noise. If you know this, please do not dig to China using a fork and your plate. The small semblance of nutrition in that snip of lettuce is not worth it. You are a terrible person if you do this intentionally in my presence, or bang pots together. Or scrape fingers on a chalk board.
The rest of my large turn offs have to do with hygiene or common sense, and are not worth mentioning.