[rewboss]

"Fucking" is an expletive -- "bad language", as a mother might say to her child -- and one you should not use in polite company. In fact, if you're not a native speaker, you shouldn't use the word at all unless you are really, really certain it's OK. In fact, it's bad enough that you'll often see it printed as "f---ing" in some newspapers and periodicals.

We're left with a very violent and graphic metaphor. It's not an idiom as far as I know, except perhaps among certain groups of people, but it is clearly a metaphor. If it were possible to actually do it, it would be a very unpleasant and messy way to kill somebody.

A much less offensive threat would simply be: "I'll kill him!" A more colourful metaphor is "I'll have his guts for garters"; it's actually no less horrible (it means, "I will use his intestines to hold up my socks or stockings") but has been used so often, it's now OK to use it in polite company. (As long as you don't also add "the F-word".)