Not really a misunderstanding, but:

Me, entering into a room of Argentinian geophysicist coworkers, without knowing spanish: “Good morning senoras!”
Coworker: giggles. “Senores”
Me: “Why?”
Coworker: explains gendered nouns in Spanish.
Me: “Ah, OK, let me try that again; Good morning senoras!”
Coworker: “Oh, fuck you…”

Just typical banter between coworkers who had been working together for years.