Teemo of course. He is designed to be a pain in the butt. Dem shrooms, poison-AAs, blinds and dat annoying voice... although I like his badgerdance.
Another one is Yi. Alphastrike seriously needs a longer cooldown. A Yi who is not stupid and doesn't aim it at you can harras and farm for days while being totally safe. --- Currently playing: Persona 4 Golden & Disgaea 3 Absence of Detention