Short for King of Substance Abuse, That one friend who gets completely shitfaced and abuses multiple drugs almost everyday.

Note: There is a "B" instead of an "A" because the "A" is very quiet in abuse.
BRO 1: dude, did you hear about what john did last night at the party?

BRO 2: yeah well he is the KOSB so I can't say I'm surprised...
by therealKOSB October 09, 2011

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