Recently I've heard couple of interesting idioms one of which was "Make yourself scarce or I'll polish your mug". So, I was wondering is it really used like that? I've heard of "Make yourself scarce" before, but "I'll polish your mug" is the first time I heard it. Does it sounds natural? Can I actually use it? Or will it be just funny if I say it?
I wouldn't consider that to be offensive- more like jocular. Mug is a slang term for face. To "polish your mug" means he's going to beat you up.
Presumably the "embellishment" to your face will consist of a bunch of cuts and bruises.