So I was at a fancy Japanese steakhouse in Tokyo recently and the waiter kept asking me if I was ready to order, and I couldn't make myself understood that I wasn't ready. I don't think he was trying to be pushy, he was just trying to be attentive and a good host.

Remembering back to some anime I've watched, I threw out "chotto matte-yo" to ask him to give me a minute. He looked a little abashed and backed off quickly. I hadn't meant to be rude or too straight-forward but didn't realize what I had said. I should have said "chotto matte", but what did I know? Anime had steered me wrong.

So here goes:

-yo at the end of any statement adds emphasis and is considered forceful and somewhat crude. So whenever you hear someone in anime say something ending in "yo", its because they're making a firm or strong statement. That's why "nan da yo" is often translated as "what the f*ck?". Literally it still means "what is it?", but with some force behind it.

Some anime examples:

da-tte-ba-yo (in this word, both the "tte" and the "yo" are emphasis words)
de gozaru yo (from Kenshin, means "that it is", but with emphasis)

Any native speakers or learned-gaijin, please feel free to correct me or add to this.