Yeah they are a brittish thing. Their generally delinquent youths but some are older than the average teenager. The general stereotypical chav is on benefits, has a violent temper / likes to cause trouble with the rest of the public - IE egg windows, play loud music till early hours of the morning, destroy property etc. They usually have the attitude that people should "respect" them for whatever reason and if you don't they make your life hell. They spend half of their time causing trouble and the rest smacked off their face.
In my opinion their arrogant little **bleep**s who need to learn some respect and manners.