People who don't fly often and dont have a clue. They don't have the right ID, or they don't have it out, and hold up the entire line hunting for it. Then they walk six abreast so you can't pass them. Or the people who STAND on the left side of the moving walkways and won't move to the right, even though it SAYS STAND RIGHT, WALK LEFT.
The people who bring too much stuff on with them. People who can't manage their own luggage and expect someone to help them. People who whack you in the head with their bags because they have too many as they go down the aisles, and it REALLY makes me angry that the gate agents let them carry all that crap on! people with kids who RUSH to preboard, then hold up everyone getting off becuase they want to be first off, even though they have a gazillion things to deal with.
People who put their seat all the way into your lap just at the beginning of meal service. People who kick your sat the entire trip. People who let their kids stand up and drool all over the seat back and cough or sneeze their bugger faces at you.
People who BATHE in perfume, reek of stale smoke, or have BO.
People who have seats in the back of the plane and put their roll-on in the first overhead they come to.
People with assigned middle seats who take the aisle seat and then get pissy with you about moving.
People who can't fit into their own space and expect to raise the armrest to take half of the seat you paid for as well.
I could go on, but you get the picture. I don't mind anything about flying, it's the other passengers that get me going.