Just for fun, and on a continuing basis, I'm going to start a phrase and anyone reading is encouraged to post the completion in the comments. I will be posting the first completion in the comments myself.

This particular phrase beginning is clean but the end will almost always be dirty. My son ran across this phrase while playing "Duke Nuke 'Em". I had to explain that the phrase had been around since at least 1980 (I used it while in the military).

Here we go:

I'm going to rip your head off and…