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1.
The ability to perceive the signs that a neighbourhood or area has gone over to the crack trade.

The ability to perceive serious hard drug use in others.
"Wow, my crackdar really must be off! I totally missed that girl's track marks and the wasted guy passed out in the parking lot."

"Don't you know she's got a serious drug problem? Dude, what's wrong with your crackdar?"
by MonsieurT August 08, 2008