A fartbanger is defined as a 4 cylinder (4 banger) front wheel drive car equipped with an oversized muffler. It literally sounds as if someone is farting in an empty beer can. Typically these vehicles are driven by inexperienced drivers who derive thier skills and value set from playing Grand Theft Auto and watching Fast & Furious.
In example, any older model front wheel drive car is a perfect candidate to become a Fartbanger. Just hacksaw off the factory exhaust, slap on a crappy piece of junk megaphone type muffler and viola... You have a Fartbanger. Oh, don't forget to add a really dumb looking spoiler and maybe some stickers too.