Someone that is such a cunt, they are literally emanating cuntness out of themselves at a very high speed, therefore becoming a cunt rifle.
Someone that is always being a cunt and looks for opportunities to be a cunt, shooting others down.
Tasha turned into a cunt rifle last week after her PMS made everyone hate her.
John: What's up Sam?
Sam: Hey fuck you John, you can suck a dick.
John: What the hell... fucking cunt rifle.