Acting like a complete idiot. Presumably "the blue crack" is Drain-O Crystals. "Have you been smoking the blue crack?" is thus analogous to "Have you been drinking turpentine?"

Note that this usage pre-dates the use of "blue crack" as slang for Tylenol PM.
"A customer asked me today if I could see her computer screen through the phone. I asked her if she was smoking the blue crack."
by luvcraft2 May 22, 2009
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