Put it at the end of a prying question in an edit, so the question sets up the refusal, then follow it with an awkward moment beat before cutting to the next scene. For a longer exchange, open with Eh Eh Ehhhh as the setup, then let this clip close the conversation.
Über diesen Sound
This is a short Spanish voice clip, just over six seconds long, built around one dry spoken line delivered in a calm, matter-of-fact tone. It lands as a deadpan brush-off, funny because it sounds polite while clearly closing the subject, and it leaves an awkward pause that makes the other person back off. The flat delivery is what sells the joke.