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1. peel a cap
To shoot someone in the head.In the process there skin is peeled from the bullet entry.
I love blowin mothafukaz heads off.Today i gotta peel a cap!!
2. peel a cap
Killing someone by means of shooting in the head, causing their cranium to take on a look as if it were "peeled" back.
One wrong move and your cap's peeled" -- Ice T

You're too drunk and high to peel a cap. I'll do it. Bitch, what are your final words before your cap gets peeled
3. peel a cap
to shoot a gun, that is to 'peel' a cap from the chamber or clip.
I'ma peel a cap off at this bitch
or
I'm gonna peel a nigga cap.
4. peel a cap
To shoot someone in the head with a firearm: cuz if you shoot someone in the head while they're wearing a hat, you 'peel' their 'cap' off.
To 'peel a cap' in "Hood Took Me Under" by Compton's Most Wanted:

"This fool I thought was my homie, dropped a dime,
So I gotta peel his cap with the 9."
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