An insult usually directed at an apple enthusiast which is a reference to the fact that mac books are sold to drug dealers in order to obtain drugslike crack.
Hobo #1:
Yo! Hey Benny! Whatchoo gonna spend that money on?!
Hobo #2:
(panhandling on street corner) Aw, y'know, just--
Hobo #1:
YOU GONNA SPEND IT ON CRACK?
Hobo #2:
What? Dude, shut UP!
Hobo #1:
You gonna spend it on HEROIN? METH?
Hobo #2:
Aw snap. I do believe I was just crackblocked.