Otherwise known as Death on Wheels.1)2) They may only be worn with tight neon leggings and/or a nylon workout suit.3)

1)
Four wheels, to be precise.
2)
Per foot, that is. Unless you have a strange pair of rollerblades. Could be 3 per foot though.
3)
Unless, of course, you're Batman, in which case your leggings may be black.