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3.
1) Someone who acts like someone cool in public but when with friends is completely different.
2)In use to why a person may act strange or random.
1)Girl 1: Yeah, he's actually quite nice when he's not surrounded by people.
Girl 2: Ah, so he's blue crack.

2)Girl 1: AH! Look, there's a singing goat!
Girl 2:........
Girl 1: That crazy goat.
Girl 2: You're so on blue crack.
by angus the superduck March 05, 2005
 
1.
Slang for Tylenol PM - and the similar generic store-brand variations of the same - when used as a recreational drug.

Contains diphenhydramine and acetaminophen - the latter should be avoided. It's *really* bad for you when used in excessive amounts.

I doesn't contain dextromethorphan, so it's not technically a robotrip, but roughly similar.

Nonetheless, you can get high off this stuff. Tastes kinda frosty-minty and strong.
It's blue - it's liquid - and you can buy it in almost any drugstore.

A cheap and legal high - Blue Crack.

It's HELLA dangerous, though, because of the acetaminophen. Try something else!!!
by kire October 23, 2007
 
2.
a strain of marijuana, cross between Blue Dream and Green Crack
"I smoked Blue Crack out of this 6 foot bong the other day and i was baaaaaked"

"Yo dawg pack sumo o' dat Blue Crack shiit"
by alienjiz1990 November 27, 2009