I think it's dumb when people do this to Teemo players. There are some situations where he's a great pick. He counters a lot of top laners, even if he's pretty bad against some of them. Even mid and support he can be amazing. Imagine, every Jhin crit or Jinx minigun onslaught - totally negated while you auto them and either out-trade them or kill them. Imagine how pathetic Talon can be when his combo is completely interrupted. And Teemo in a lane against a melee range champion? Oh, you can dominate the shit out of them in lane.
But no, people hate Teemo because he's burned them too many times, and a couple of Teemo players think they're the best thing on the rift since Riot's decision to remove the Blue Pill. Yeah, sometimes they can be assholes, but I never understood why people thought banning them was their best option. I mean, if these are the toxic ones, what makes you think this is what your team needs? Some guy flaming people and asking for reports in all chat? If he's toxic, mute him and report him later. If he's trolling, report him for griefing or unintentionally feeding. Later. No need to sabotage your team's chances by banning the pick that some guy wants. Explain why you think Teemo is a bad idea (i.e. no tanks in team comp, he's trying to support against mf/varus/whoever, etc.) and if he doesn't listen take care of it later. For all you know, this is the best Teemo in your division and is going to whip any top laner.