What grinds your gears the most?
For me it's that even after all those years, people didn't learn to be aware of their sorroundings and take cues from other players. Getting backstabbed, letting a teammate get backstabbed. Being oblivious to cues like stabs stabs from teammates pointing behind them, indicating there is an enemy. Prioritizing wrong enemies. Ganking up on one enemy, when there are 3-4 or more enemies within a few steps of them.
Recently, it's also dedicated throwers that kill you with 2 hits with a regular throwing axe and always have teammates helping them.
Third worst thing, for me are archers, who go lone wolfing and get killed by enemy archers, while trying to shoot infantry. Completely useless cunts. Also cavalry either team bumping you or just riding by like nothing's going on. There are so many ways for cavalry to help out the team, riding up close to an enemy that's killing you to divert his attention, diverting archers from infantry by riding close enough for them to notice you but not too close to hit you etc. , yet most do none of them.