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.
"Err, no fanx - it's full of gack!"
Professor Commentary on test: GACK! This is not proper terminology.
"GACK!, be quiet now! Or I will leave!"
2A some what derogatory name for person under the influence of crystal meth.
or Thats some killer Gack!"
2. "That guy is a total effin gack." or "Quit being such a gack, your going to get us busted!" or "Never bring that gack over to my house again!"