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Uranium by product and gouda cheese mixed together to create the one and only gack. Gack has the ability to be a tasty afternoon snack or can also perform shit rockets. shit rockets will expel chunky poo from your bum at speeds exceeding 200 mph, it will, rip your rectum in half.
WOW! I ate gack last night! and it blew my ass in half!
by goo goo the magical elf November 10, 2010
A really nasty substance. Like ear wax, saliva, boogers etc.
"Dude! Your ear phones are full of gack!"
by paleteroJ March 27, 2010
The first retching sound a cat makes when it hacks up a hairball.
I heard Morris gack after giving himself a tongue bath.
by the_great_waldo October 21, 2009
Another word for cocaine
Come on lets go and buy a big bag of gack
by tomo April 26, 2004
Crank, lower quality methamphetamine not the higher quality crystam version but the stuff that is brown some times and burns like hell. There are 2 types of gack. One eye and two eye. One eye refers to the burning pain and tearing in the eye after snorting. Two eye gack makes both eyes burn and water from snorting it in one nostril.
"I did some gack last week and I still feel like shit!"
by PharmaPharmer December 30, 2004
v. - to steal, snatch, grab, or otherwise take something into one's possession
I was thirsty, so I gacked a Coke from his fridge.

If you like the ring, gack it when the clerk turns around.
by BlackArthur January 02, 2004
Where I come from, Gack always refered to the residue left over from smoking bongs or buckets.

Gack was scraped out of the cone or the bucket 'head' and ususally chucked in an ashtray. However, those on the dole and rather skanky used to smoke this gack by wiping it on a rizla.

They were known as gack heads. Nasty.
"Duuuude, take a lug on this..."
"Err, no fanx - it's full of gack!"
by Powdermonkey May 24, 2006