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1.
An adjective. A slang word for use in place of such words as "cool", "awesome", "crazy!", "evil!", "great!", "rad!", "Viktor-Tsoy-related!", etc.
The Crazy Sushi forums are so boshetunmai!
by One Who Is Boshetunmai March 28, 2003
 
2.
other variants may include
"be worthy" or "don't sell yourself"
(reported to be translations from Mongolian and Korean)
"Boshetunmai!" can be used alone
by Mavra January 04, 2004