Place it right after the friendly greeting or bold claim, so the denial cuts the setup short. Open with Sudden Suspense to stretch the pause before it, then follow this clip with No No Wait Wait for the other person's quick backtrack.
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This is a short spoken line lasting just under three seconds, stating plainly that the speaker does not know the other person. The words are simple and direct, leaving no room for a friendly follow-up. It feels awkward and funny at once, like catching someone pretending to be close, and the short, firm rejection lands harder than a longer argument would.