What has been interesting for me sometimes is people assuming I don't speak Japanese because I don't respond immediately. Once at a drycleaners, dropping of some femine things for my roommate, the clerk asked my name and address. I thought it was odd of the clerk to ask for those (based on my experience at other dry cleaners in Japan), but before I could reply, she started in broken English in an irritated voice, asking the same questions.

Some the assumptions made in Japan cut both ways, as some embarassed foreigners have found out ('assuming' they knew the neighboring Japanese spoke no English).