Thresh

If your teammate has no idea how to click his lantern, nope.

His lantern is so annoying to play against.

He offers a lot of potential big plays between hooks, lanterns, and flay (for the dash interruption). He's very flexible in how exactly you use those things, and so he can cater to a variety of playstyles. He's not necessarily the best pick for any particular playstyle, but he's quite popular at high levels of play because he can adapt to a lot of situations and be useful.

How effective he is will vary widely with your skill with him though. (He also typically builds relic as a support item despite technically being ranged, and so it can be a learning curve for new thresh players to actually last hit properly instead of relying on the execute.)