My work once sent me to Madrid. I only have some high school Spanish.
I had a cold at the time and soon ran out of cough drops. My coworker told me where I could buy some more, and what to ask for.
When I got to the store, apparently I misremembered what he told me to say. I said to the woman, "quiero caramelos de mentales."
She looked at me confused. I tried again, slower: "caramellos...de...mentales?"
She seemed a bit alarmed. She said something in Spanish. I said "lo siento, no comprendo."
She called over her coworker, who asked me "what are you looking for?"
I said, "cough drops." She looked confused. "Cough...drops? What is it?" I tried "caramelos de mentales" again, no success, just confusion.
Then I remembered I had some wrappers in my pocket so I pulled one out and showed her. Suddenly they both beamed with understanding. "Ohhh! Caramelos mentolados! You were asking for 'brain candies.' She thought you wanted something illegal."