Teenager arrested over tweeting at Olympic diver - CBSSports
Because it's too too easy for people to overreact, and attach way too much importance to 140 characters.
So what if the kid said something mean. It was just words. Just. Words. And compared to many blog comments, posts, other tweets, not really exceptionally mean tweets. Just childish and stupid. Jails are full enough. If we start putting everyone who ever utters some mean words in jail, there will be very few left uncaged.