1. People who ignore the POH - notably those who add a few knots for luck.
2. Egos and arrogance - pilots who don't accept they are fallible.
3. Carburettors - why do the manufacturers still peddle them?
4. People who believe the only GA aircraft type is a Cessna/Piper.
5. Pilots who bring an aircraft back with minimal fuel and then expect the next pilot to fill it up.
6. Kneeboard/headset discussions.
7. "How fast is your Arrow?" discussions.
8. People who cut you up in the circuit.
9. Flying clubs where two geriatrics who have hardly flown in the last decade still have overwhelming influence.
10. Pilots who extend flaps/gear etc at limiting speeds.