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1.
A phrase used when one either: (1) Does not know what is going on, (2) does not know what just happened, (3) does not know the answer to a question, (4) or simply would like to break the silence.

Usually, when said phrase is used, it is followed by a near-endless spree of other quotes such as:

1.) Psh, I don't even know.
2.) Aw hail naw.
3.) Aw hail naw, cracka.
4.) Mmm hmmmm!

The phrase "I don't even know" is best used in the classic "I don't even know" speaking tone, which may only be properly "voiced" by either a colossal, Japanese monster, a small cat/kitten, or a constantly hyper-active younger brother.
"Matt, why aren't you talking?"
"Psh, I don't even know!"
by I Gojira I October 31, 2007
 
2.
This clever phrase was invented by the bright, young man, Chris Allen. He patented the phrase on July 15, 2007. The phrase, "I don't even know," is quite an unique expression. It can be used as a extreme adjective to describe the undescribable, or it can be used to express thoughts of confusion. It can also be used as a verbal space filler. This phrase will go down as one of the best phrases in all of phraseology history.
"Man, that girl is as ugly as... i don't even know."

"What's going on tonight, bro?"
"I don't even know, man."

((When in a conversation and an awkward silence comes up))
"Yeah, well, I dont even know."
by C.Allen February 23, 2008