Darius, Singed, Volibear, Wukong, Teemo.
Darius because he is ridiculous and too easy to play so bad players can beat you with him.
Singed, shut down early he is not a problem and he doesn't snowball unless he gets ahead however if he does forget that comeback. That and if you focus him someone else is doing more damage to you.
Volibear, very easy to counter with ignite/chogath/darius and many more combos however he starts incredibly strong and will force you to play cautious if he is in your match it will always go longer then normal.
Wukong. Focus him? ignore him? im annoyed just thinking about it.
Teemo. Probably easiest on this list to counter and if picked ill likely win just wont have much fun doing it lol.