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1.
Guak: adjective. Can be used in place of many other adjectives. Depending on the context of the sentence it has several different meanings, but it is almost always a negative connotation. It can describe a person, place, thing, concept, idea, belief, etc. It is usually used in place of: wack, silly, ugly, dumb, uninteresting, stupid.
1. "He is so guak."
This could be implying many things: He is wack, unattractive, doing too much, has a bunk personally, boring, etc.

2. "That purse is so guak."
Stating that the purse is ugly in some kind of fashion.

3. "You are so guak" (When referring to a friend)
Usually to replace stupid or silly, like when your friend cracks a joke, or something of the sort.
by Michelle Denise Kramer February 26, 2008
 
2.
money or cash; just another way of saying "paper"
Counting my guak, all in a days work
by Mandygirl October 27, 2005
 
3.
guak is an acronym for " give us another kiss "
I was lying in my bed attempting to go to sleep. Outside in the street I heard a young couple talking. I heard the guy say " guak "
by St. Ias October 29, 2005