From the source of jungle/dnb lingo, the Junglist Dictionary:
Bo! - Simulated gunshot. When a tune is big, say this loud if you want a rewind. In Jamaica, people used to fire blanks all the time when a tune was big.
For a definition of rewind, see the Junglist Dictionary you lazy bastards.
"GET OFF THE DECKS YOU FUCKIN LOSER!"
*DJ drops a hot fuckin tune*
*DJ drop kicks AK1200 in the face*
"BOH! BOH! BOH!!!!!!!!!!!!!!"
As seen in the Simpsons episode "Burns' Heir," when Burns tried to convince Bart that his family doesn't miss him, and hires actors to portray them on a video feed. But, the Homer actor flubs his lines, saying "B'oh" instead of "D'oh."
Marge Actor: (odd voice) I am glad he's gone.
Lisa Actor: (odd voice) As am I.
Homer Actor: (drops) sandwich B'oh!
Saying this phrase to another Simpsons buff displays superior knowledge of Simpsons trivia; said usage also points out the over usage of the phrase "D'oh" and avoids obvious simpsons clichés.
Origin: In Simpsons episode 1F16: "Burn's Heir", an actor portraying Homer mistakenly exclaims "B'oh" after dropping a sandwhich while trying to convince Bart the actor is the real Homer (Saying "D'oh" would have been more realistic).
SimpsonsBuff1: "Dude you just dropped your beer"
The term originates from the Jamaican/Reggae culture where a gunshot was used to signal/call a rewind of a big tune. Now, yelling BOH! or BWOH! is a common vocalization used to affirm the selections/sound of the Selectah/DJ.
Trainspotter standing all night with his arms folded right in front of the DJ booth finally hears an exclusive dubplate he recognizes, yells "BOH SELECTAH!" - and promptly raises his lightah!