Players who play ranked games and deliberately troll. If you're going to troll, play normals. People like that are why it's almost impossible to get out of bronze. There should be a way to leave games like this without penalty and then permaban the offenders.
The majority of trolls I've seen didn't start the game trolling. Yesterday had a Rumble on the opposing team that went Mid after Vlad, their first pick, was going top. When they got into the game Vlad flamed Rumble and told him to "EFF OFF" he's taking mid, because he didn't like his top match up. So Rumble, instead of being an adult and just going top trolled. Neither player would back down and go top so their team ended up losing badly.
This has been my experience with most trolls - they didn't start the game that way, but flipped when circumstances "made them do it" and that's the excuse they use. "X made me AFK" / "X took my CS / blue buff etc" - So they didn't go into the match thinking "I'm going to troll", but instead just responded to the negativity of the situation.
