When a person (intentionally or unintentionally) says or does something that blocks the acquisition of crack by another.
Can also be used for any illegal drug.
See also, cockblock
Yo! Hey Benny! Whatchoo gonna spend that money on?!
(panhandling on street corner) Aw, y'know, just--
YOU GONNA SPEND IT ON CRACK?
What? Dude, shut UP!
You gonna spend it on HEROIN? METH?
Aw snap. I do believe I was just crackblocked.