Most people have at least one pet peeve. If you give it some thought, you should be able to think of one thing that other people do which really annoys you.
Sure, every person is different, so the bad habits that annoy you most might not bother your friend or coworker. However, there are definitely certain bad habits that are annoying to large numbers of people.
1. Nose picking
Everyone picks their nose at times. Not everyone picks their nose in a public place where others might see them, though. Many people really dislike seeing someone pick their nose. It is particularly offensive when the nose picker picks with relish, as though they were embarking on an exploring expedition to some unknown land.
If you need to pick your nose, do it in private to avoid upsetting those around you. Bear in mind that your car is not a public place. If you decide to pick your nose while commuting, people in other vehicles on the freeway will see you digging for gold.