refers to the ignition cap at the base of a cartridge for a firearm. "bust a cap" means break the cap by pulling the trigger, setting off the explosion that propels the bullet

A person,who always tells such obvious things that people around think he is really stupid.
Caps are usually ridiculed.

Capping was a word used back in the late 80's early 90's that described a form of word battle. Saying someone's shoes were bought at K-Mart would be a form of capping. Basically it's a form of putting someones cloths or style down. It was common to hear someone say "ohhh you got capped on!"

Coming from twitch.tv Kappa meaning joking, no cap means no joke

part of shrooms

To be shot, shot.

(from skater slang)
means that something is the truth or that you're not lying.
the phrase was ruined by tiktokers and just 12 year old kids using it in general