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1.
A word used by the underground culture of children ages 14-16 that is equivalent to the word owned, pwnd, or o(p)wnage. It is used whenever an individual "owns", tells off, or basically proves their superiority to another or many others. An exclamation point is usually added at the end of the word to emphasize the emotion represented when you use this word and show others how you just owned them. A "yeah, uh" can also be added for emphasis. The boom in daboomchi is accentuated for a better effect. So, in theory, you would say it like this, "Yeah UH daBOOMMMchi!!" This word/slang term was brought forth by dagrlz, especially Number 1 and 4
After Ana and Becky ditched Jessica at Six Flags, they went "DABOOMCHI!" in her face.

Mom: Why were you walking around with only a bathing suit on?
Becky: Cause we're hot! Duhh
Ana: YEAH UH DABOOMCHI!

-guy gets shot in the movie-
evil guy: DABOOMCHI!

becky: Abe Lincoln was the first president of the USA
ana: Uh, no he wasn't
becky: yeah he was
ana: ayo dookie was abe the first pres?
dookie: no...
ana: YEAH UH DABOOMCHI!!!

by Shorty So Seductive August 08, 2006