Someone who thinks its clever to spend £5,000 tarting up a £50 piece of crap that is one MOT away from the junk yard, fit it with a stereo pumping out more power than the engine, remove the suspension, destroying what little handling ability it had, and a set of wheels that look like rejects for the London Eye. The exhaust must look like it's been robbed off an F15 Eagle. I have yet to find out what mod they do to the drivers seat to make them all drive canted over to the left like their spine is buggered.
A chav, charver or scally under the age of about 12. Worse than adult specimens because they know the child protection laws better than the average lawyer, and hence giving one of the little darlings the dry slap he/she so richly deserves will land you in court faster than you can say "knocked off PlayStation".