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1.
The origin of bust a cap meaning to discharge a firearm has become a general threat of violence with the implication that a gun will be involved. To threaten to bust a cap in someone's ass is also not intended to be anatomically specific, as kick ass or whip your ass are not descriptive of specific actions against someone's posterior. Ass as in "your ass" "my ass" etc refers more to the whole of the physical person. Further appellations such Honky, nigga, nigger, white boy, bitch, etc. are context dependent and may not have racial or gender implications.
"I'm gonna bust a cap in yo ass" "I would never bust a cap in your ass" "Please don't bust a cap in my ass" etc
by Doc@demon June 21, 2006
 
2.
"Bust a cap in yo ass", To shoot a bitch in the ass with a gun. Usually used by niggers but also used by the occassional poser white boy.
"Bitch im gonna bust a cap in yo ass if you dont shut the fuck up"
by Bojokomofo February 05, 2005
 
3.
shoot em up
im gonna busta cap in yo ass
by devin February 14, 2004
 
4.
it means to put a bullet in a person's ass for acting like a lil bitch
Im going to bust a cap in your ass for being a bitch.
by Fidel May 09, 2004
 
5.
For a bunch of 'homies' down on the 'west side' to kill a whitey
Yo, Imma bust a cap in yo azz, Honkey
by DaQuisha August 20, 2003
 
6.
Something that dickheads say thinking they're saying "I'm gonna shoot you" but they're really saying "I'm going to ejaculate in your ass during anal sex" (usually homosexual)
I'm gonna bust a cap in your ass white boy!
by joveblue July 10, 2004