He has range, so no need to engage.
He can put mushrooms up to block your path and slow you along with anyone else in the area. They explode upon impact or if you destroy them, which is absurd.
He can speed up if you catch him
His poison shot does huge damage early.
He can always go invisible.
His basic attacks can do huge damage and I've seen him 1v1 everyone in the game.
Counters tanks, counters pretty much everyone minus Cho.
Keepe6 votesEver play Teemo vs a Garen who knows what he's doing?
Pre-Six, a good Garen will sit back, relax, and farm under his turret. Post Six "Nice blind. I can wait- Aaand Auto. Spin. Ult. Dead. Good bye, rat."
In short, when you complain about him like this, and say Teemo counters tanks and pretty much everyone, it shows that you're either A, just complaining for the sake of complaining, or B, not at all versed in how to fight a Teemo. If the latter, it's understandable as he is very rarely picked. Since he's not, you know, too viable.
D3M4L1S2 votesI agree with most of what you said, I play blind solo, he is popular as hell.
Great Muta1 votesWhat if the Teemo knows what he is doing?
These remarks like this rely on the opponent being brain dead.
Keepe4 votesIn my specific scenario? Teemo can't run. He has a MS Boost, so does Garen.
In short, Teemo may hurt like a witch, but he is still Teemo, which is to say a Squishy little dead rodent.
So. Punch him in the face until his health bar goes away.
Great Muta1 votesI actually just beat the snot out of a Garen with Teemo and today was the first day I ever played Teemo. I Q'd and E'd him nonstop and placed the shrooms with the minions and near the turrets. By the end of the game, with 2.37 AS per second with 300+AP, he was done.
TyrekGoldenspear3 votesThe Garen didn't know how to play against Teemo imo.
I would rush 
then Black Cleaver, while farming under turret and popping in and out of bushes.
By the time I get tanky I couldn't care less about Teemo's DOT.
If I get on him he's dead. I can outscale him as Garen.
agbudar2 votesteemo CANNOT trade with a garen at lvl 6 period. unless teemo somehow magically got 4 kills. but a half decent garen will not bother and simply get xp/gold under tower. and dive at lvl 6 easy peasy.
teemo by definition pushes lanes out.
TyrekGoldenspear3 votesThis.
I love destroying Teemos who think they can make my life a living nightmare as Garen.
Swiftstrike43 votesAnd 
counters the core of his kit. Once you hit level 9 and you haven't fed him too much he is pretty much useless.
Perma CC2 votes
Catastrop2 votesFor AD, to auto win lane.
For AP, what the fuck you're AP, fucking kill his ratty ass.
President Swa1n1 votesTo add on to what everyone else has said, his teamfight is absolutely WORTHLESS if he isn't mega fed by late game.
agbudar1 votes
junglers say hello freelo
Great Muta1 votesOh no one ganks top lane in Low ELO's, at least not on my team.