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Related to horn in: Scur, toot own horn
To intrude on someone or something. Please don't try to horn in on my phone conversations—they're none of your business.
horn in (on something)
Fig. to attempt to participate in something without invitation or consent. Are you trying to horn in on my conversation with Sally? I hope you are not trying to horn in on our party.
To join without being invited; intrude: The new supervisor horned in on the discussion. We were talking privately when a coworker came over and horned in.