I think the word 'chav' almost certainly does have its origins in the Romany word for boy. In my own village in Sussex, which has one or two families from Romany/traveller stock as residents, 'chavvy' (boy) is used by many people. When my son was very small, I'd often be greeted in the High Street with the friendly words, "Hallo Will - how's the chavvy?" - and not just by the Romany family members.

Now, I can't think of any other word which could form the basis of the word 'chav' - acronyms such as C H A V are often wrongly attributed as origins, when they're really dubious backformations.