A donk is essentially a big old American car, although any will do, which is painted a gaudy colour, trimmed with chrome and fitted with 30 inch wheels. Which are generally chrome. And sometimes have spinners.
There are some benefits to donks. For example, home mechanics can now work on the underside of their car without needing to use a jack. And, that's it. There are no other obvious benefits.
There's a donk gallery below. But before we mock our American cousins, us UK based car nuts should remember one thing - we're more than capable of making a decent car look like a bag of spanners ourselves. Have a look at Speedmonkey's modified cars gallery for evidence of that.