Things like admitting when you've made a mistake, giving someone tips when he makes a mistake instead of berating him, sportsmanship in general are signs of maturity. This is not something you can expect from the target group of LoL.

A couple of people talked about things like being in a game with 10 people and relying on each other and that games tend to be long. These are all things that you learn to deal with when you actually grow up and become mature enough.

I reckon the average LoL player is pretty young, especially in lower levels. So the community sucks because people are immature, there's nothing you can do about it, except being mature about it yourself. It's a shame, such a nice game, I really love it, but things like this make it much less enjoyable. Play with friends!