It was the scout for me, then I grew hatred towards Pyro, but I now believe it to be Engineer, and it's ironic because I used to be an engie main, the reason being that atleast all other classes require some skill and timing to use, engineer pretty much does not (except for short circuit, gunslinger and frontier justice).
This is because engineers can just assemble large groups, camp in narrow areas and have a sentry rack up countless kills with no effort, it does occasionally take wit to deal with a spy in pvp or sentry buster in mvm, but beyond that, it is just a low skill, high kill strategy to play the game, i'm all for engies that support, defend and even attack, but the way some people go about it just ruins it for everyone in my opinion