The slang word 'Cap' is the shortened term of Captain, used mostly in New England but mostly found in maine, around the penobscott and Hancock county areas.
A slang term for semen, male orgasm/ejaculation(excluding female ejaculation). The term is thought to have originated from Sub-Saharan Africans having first seen a snow "capped" mountain, concluding that the mountain was covered in semen.
Originally, a kneecap. The phrase "bust a cap" originated in Northern Ireland several years before entering urban gangsta culture, and referred to the nonlethal (but fantastically painful and disabling) practice of firing a firearm at close range into the crook of the knee. The practice served, and in some areas continues to serve, primarily as an intimidation tactic, and the victim becomes a hobbling reminder of what happens to "the enemy."
I told him I'd bust a cap in his ass, but it turns out he didn't have an asscap after all, so I let him go.