Chav

If there is an award for the word of the year in 2004 it goes to "chav". There has been a lot of debate about its origins, but the most authoritative account comes in this article from Michael Quinion's site World Wide Words:

Chav is almost certainly from the Romany word for a child, chavi, recorded from the middle of the nineteenth century. We know it was being used as a term of address to an adult man a little later in the century, but it hasn’t often been recorded in print since and its derivative chav is quite new to most people.