in a section of west london, this means bad, useless, crap
"That film was BRASS" or "you are BRASS at tennis"
Crackfuck is the joining of Crackhead with fucktard, producing "Crackfuck." It is popular because of the alliteration of the hard k sound in Cra, ack, uck.
1. Avril Lavigne is a crackfuck.