Well, first of all, I need to say that if you aren't British you may not know what a chav is...
A chav is an uneducated, socially inacceptable person who follows fashion in Britain... That is what the guy on the left is. Now, the rest of the humour should be understood, but then again, I am quite vague...
Please God don't blam this!!!!
UPDATE: Thanks to the people who corrected my grammar... It's all been corrected now...