When you answer the phone in Korean, you're supposed to say "여보세요?" (yuh-boh-say-oh). This is a formal way to answer the phone. I thought that the informal version was "여보" (yuh-boh), so when my Korean friend called me on the phone I said this word to her. I was very confused when she started laughing. I later learned that "여보" is a term of endearment, so I basically called my friend "sweetheart" in Korean.

That's funny. When I first learned Filipino, I said, 'Silipan mo nga yung kaibigan ko'. What I wanted to say was 'Kindly check on my friend' I did not know that Silipan has a negative connotation when I first said that and everyone made fun of me when they heard it. In Filipino, if you want to check on somebody then the correct word for that is 'Silipin'. Silipan means to peep or to look at someone sexually

@ArianaZialcita Haha, that's what I was talking about :) 

A friend of mine made a similar mistake in French. She wanted to say "Can you do me a favor?" but she translated it from Italian, and the result was "Est-ce que tu peux me faire un plaisir?" (Can you do me a pleasure?). Not sure my English translation gives the idea, but she said something with a sexual connotation.