I would say pretty much anything that could be described as, or otherwise be found on a bike that could be described as ‘fixie’, is terrible.

some things that drive me a absolutely nuts though are these type of bars

These clamp on rear fenders


And any plastic or carbon ‘mag’ ‘aero’ or ‘tri spoke’ wheel. Especially in the rear. I won’t hate you for this stuff, but I will hate your bike.