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1.
Slang term for Marijunia (weed) commonly used by chavs and sos 'ards
Yo man get your skins out and roll me some wacky backy
by -[NM]-Raziel February 24, 2005
 
2.
slang; generically used to signify an illicit substance that cannot be procured in any ordinary means by the general public. An essential prerequisite involves an uncharacteristically underground drug dealer who conceals him/herself in little conclaves on certain un-lit side roads, selling these aforementioned illicit substances.
Hey, I saw Swathi today outside UCL. She was smoking a bit that wacky backy!
by Venkat.Thiagarajan April 21, 2010
 
3.
Used by Kurnel Krool and JTG in the song 'Wacky Backy' which talks about mums smokin weed!
"Your Mom Smokes The Wacky Backy"
by Ben May 06, 2005