To flatter or show excessive respect to someone in authority, usually to gain favor or advantage.
From American slang, likely originating in the early 1900s; the origin is uncertain but may relate to the idea of someone's nose becoming brown from constantly bowing or groveling to someone else's rear end.
This colorful insult perfectly captures human behavior—we still use it today when someone's being overly nice to the boss—and it shows how crude, physical humor can become part of serious vocabulary, proving that even silly origins can produce lasting words.
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