What is his punishment?
Get creative. And remember: there are fates worse than death.
Example!
Teemo gets chucked into a boiling tub, which Ashe then freezes with an ECA.
We turn his shrooms on a mode where he can only damage himself
LETS SEE HOW YOU LIKE IT
Whenever teemo tries to damage a opponent who is a female this happens to him, regardless of if there is a pantheon in the game : http://youtu.be/06xF46tIkmA?t=19s
Teemo suffers utter metaphysical annihilation, utterly even removing the concept of Teemo from having ever existed in the first place.
He gets locked in a room with 
. That is all.
Rumble makes him his bitch.
[Electro-Harpoon], if you know what I mean.
Friendly fire is on against him and everyone gets 200% lifesteal, spell vamp, and damage for attacking him. And the shop owner will no longer allow him on the fountain.
Oh wait, are we punishing him for something? Umm, he gets a bj... from 
teemo gets locked in a room only able to listen to 
sing on a mix tape for eternity. And people think 
came out crazy after just silence.
But his eyes are never open.
He is now sentenced to a 2 week history lecture about Shurima. With 
making it as boring as possible.
As though of a slow and painful death the women of league approaches teemo. As teemo runs for his life Ahri casts her charm and all is well and good until she steps on a shroom and the charm goes horribly wrong and hits everyone in the room. Teemo had the best day of his life and his death wasn't from the women but from all the jealous men.
Teemo automatically leaves behind a trail of shrooms, and if an enemy teammate steps on one, Teemo will take damage instead of them, and the enemy will have the option to instantly kill Teemo.
He is nerfed to death.
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his abilities are removed and he is placed on the fields of justice with both teams now hunting him, after a few hours of respawning only to be brutally murdered he may have learned his lesson.
leona tosses him up into the air. Then jinx and ashe but ult him while diana hits him with a q. Then riven comes with her sword and triple q's him into the ground
-Vi uppercuts Teemo into the air and Caitlyn shoots him down.
-"Gouge 'em Valor!" Teemo is now physically incapable of peeping at all.
-Katarina does a Mitsuru Kirijo style execution, she sounds capable of it too.
-Lollypoppy.
