What grinds my gears...
Is people who don't listen to advice you are giving them. Just lost a game because a J4 and Garen built Full AD even though they were exploding instantly in fights, ignoring anyone who asked for them to build some tank items. Which left me being the only tank as Leona. We had gotten most of the enemy based killed and then these 2 decide to jump into a 2v5 costing us the game.