Put it immediately after the talker's final word, at the cut to a reaction shot or a black screen, so the interruption lands as the punchline. If the talking starts again, follow it with Silence I Kill You for a sterner warning, or end the scene there instead.
About this sound
This is a very short spoken German reaction clip, lasting just over a second, in which a voice delivers the blunt phrase 'halt die Fresse' — shut your mouth. It lands as rude, confrontational and deliberately over the top, like a comic slap-down rather than a calm request for quiet, and it works best when someone's rambling has gone too far.