Common short way of saying, YOU DON'T KNOW!! Often followed by, "Nope, nope you don't."
Rakhi: What's up your butthole?
Aaron: Dude, idk.
Rakhi: DUDE, UDK.
Aaron: W00ts your butthole.
Rakhi: I guess
Aaron: Duh.
41π 34π
Udk is a Trinidadian slang word meaning "you done know" which also translated out of creole English means" you already know"
Evangeline: Adeline are you going to the party tonight?
Adeline: Udk ,of course, what kind of question is that?
a bastardised version of i.d.k.
either as an acronym for "U don't know" or "yoU Don't Know"
-or-
a typo of idk, ugh, or both. Creating an onomatopeoia of confused complaining
if you're not into that sort of thing, then udk