Wow.....
Tastes.....
Salty.
More seriously, I'm not super experienced with online communities as I mostly have avoided the MMO experience for the last 10 years or so. That said, I find that political commentary boards are far more trollish than anything I've had the misfortune to run into here.
Have I seen openly bad play by people? Yes.
Have I seen open feeding or otherwise trollish behavior? Yes, I even had a member of my teamspeak community AFK in the middle of a game because he felt we had lost and we had time until we could FF@20.
Have I had people berate me for my play? Yup, more than once and it tends to get me to stop playing a champ for a while.
Have I seen others bullied? Too often. I've even joined in defending them occasionally, including one match where by chance a level 23 Annie ended up against a Silver 2 player midlane. The poor Annie was getting crushed, and when one of her teammates took to all-chat to complain my entire team defended the player. We did that later when our Silver 2 ended up against an unexperienced Karthus.
The community is what it is. You have a lot of angry young men playing this game and unfortunately the fact that they are safe from receiving a beating if they mouth off they often unleash in game the anger they have about being picked on in real life. They have no fear of anyone because of the anonymity of the internet. It breeds bad behavior.
Riot could try to reign it in, but from what I've seen their methods have been largely incremental. They fear going too far and therefore aren't forceful enough about stopping the bad behavior. And if you try to hard to reign in another player you run the risk of being reported yourself.
My best advice is to remember that this is a GAME. Take your own play seriously, but don't allow the antics of others to get to you. There are going to be trolls and some will be like the Teemo you mentioned who just watched you die. It happens. Sometimes it happens because a bad player decided to betray his team just so he could complain. All you can do is concentrate on your own play.
I do hope you can find some good people to play with. I recommend finding a teamspeak community. The better ones are great fun and very supportive of other players.