Notes:

1. gak
Speed, meth, twick, crank, methamphetamine, Desoxyephedrine.
(Ack! we’re out of gak.)

3. Gak
popular slang word for coke or blow.
(Man, let’s go line up a couple of phatty gakkers bro.)

5. Gak
slang for cocaine – from the nauseating effects of doing too much, causing retching after a hefty snort.
(man, that gak last night was cut, I was nearly blowing chunks.)

…And to backtrack…

2. gak
A popular Nickolodeon slime, available in many variations such as glow in the dark, speckled, cocoanut smelling, etc. Useful for making fart noises, grossing out friends or as sexual lubricant.
(Sweetie, we ran out of KY gelly, go get some of your step daughter’s Gak.)

4. Gak
A old guy who plays a gum leaf to attract children to his white ford falcon to rob them of their childhood!
(Backs to the WALL! Gak’s on the PRAWL!)

http://www.urbandictionary.com/define.php?term=gak