[MMM]

I know two guys in a very similar situation. One guy is Japanese and the other is American. The Japanese guy invited the American guy to travel and stay with him in Japan for summer break...about 3 months. The American guy had studied some Japanese, and was at least aware of some of the cultural basics.
I happened to be in Japan at the same time, and we had arranged to meet up a couple times (they were in Wakayama, and I was in Osaka, and they wanted to come to Osaka anyway. Anyway, before the trip I said "3 months is a damn long time to spend with ANYBODY. Are you sure this is a good idea?" They were sure...so I get a call in Osaka..."Can my friend stay with you a couple days?" (from the Japanese guy). By the end of the three months they were no longer friends, and I think it was about 2 years before they ever spoke to each other again.

I agree with Jason. The person who is going to be annoyed and embarrassed is you, and that gets old quick...so be careful.