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."
a word of expression to when you give up on comprehending someone's words of ignorance, stupidity, absurdity or are too exhausted to formulate a proper response.
Commonly seen in TikTok comment sections in replies to lazy attempts at humor, overconfidentally incorrect statement, or an over-the-top comment or when someone completely misses the mark on something.