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1.
A unique attribute of the female gender and gay males; a sense that seeks out a man’s penis as if guided by radar.
Erin's junkdar was honing in on Casey. She really wanted some action and nothing was going to stop her.
by The Caseman October 31, 2006
 
2.
The uncanny ability of a junkie/drug user to locate substances at any given time or location
Billy's junkdar struck again: we were having a good time at the bar and next think you know he's got an eight-ball. He ruined another 'beer only' night with his junkdar.
by Scumberry August 21, 2006