It stands for; Must be smokin weed! Someone who was doing crazy shit while under the influence of weed.
*Zoe* Did you just see what the kid was doing?

*Tabitha* Dudeee that kid M.B.S.W!

*Zoe* Yeah, He must have been!

M.B.S.W.
by Tabithaftw November 21, 2009
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