I think the reason I personally hate Teemo so much is that he is totally binary. Either he 100% counters his lane, gets ultra fed, and wins the game... or he gets completely wrecked, feeds, and everyone complains because Teemo is just the worst.

teemo's soo much more annoying to shaco, at least shacos don't spam traps their jacks only last 60 seconds teemo's last 10 times as long and hurt a ton more. not to mention most of the time u won't die to a shaco in a 1v1 cause he's fairly weak teemo on the other hand just jumps around throws a few darts and slowly kills you

Hybrid Teemo builds are brutally easy to get rolling and take a lot more effort to defend against. An ADC gets Blinded by Teemo and can't punish him properly. Teemo can escape from a lot of bruisers. Mix of AD and AP will give tanks fits as they try catching him. Most APs will get hurt way too badly fast by Teemo to burn him.
It's not just the shrooms, although they themselves are bad enough and give Teemo far too much map awareness for free on top of the poison and slow they do.

I'd rather ban Teemo than Kassadin or Darius.