Everything that bothers me stems from people who are oblivious to how their actions or lack of manners affect those around them. Self centered narcissistic tendencies. Essentially a lack of empathy.
People who eat with their mouth open. Its disgusting. Downright repulsive if they make slurping, sucking, smacking, or munching noises as well.
Bad breath. I dont care if you only gargle listening, never brush, never floss, and your teeth are butter yellow with plaque buildup. If your breath is nice then you're fine. But if your breath smells like you just ate lunch out of a toilet bowl stay away, just talk at me from the other side of the room.
Anyone who shits while on a plane. I did not pay money for a vacation to be locked in a flying can full of your intestinal perfume. Go before or in between flights on a layover. Do not make every single other passenger suffer through your recreation of a burning dumpster full of baby diapers at 30,000 feet with no escape.
Jumping back to the narcissism mentioned earlier. There are nearly 8,000,000,000 people in the world. You are only 1 of them. Take a shovel, go out back, dig a deep hole, and leave your grandiose sense of self importance in that grave. Altruism is far sexier than any job, material possessions, or amount of money you could ever brag about having. Could go on, but those are the biggest peeves I have.