I've found it's not that hard to impress Japanese people with knowledge of the language. I always deny it, though. Partially out of humility, but mostly out of the fact that their English is usually light-years ahead of my Japanese. I do think I'm improving a little though; I completely understood a conversation completely in Japanese about nengo that I had with my cousins at a restraunt, and it was kind of cool seeing everyone else at the table but three of us conversing and wondering what the hell we were talking about. :)