[virtuah]

when they think you don't understand the language, they show their true colours.

No truer words were spoken.
Sorry, this is off topic but I have to throw my 2 in while I can.
I use gaijin with friends and family, but take offense when called that by strangers (which can easily reach double digits on any given day). Even if it's not used with malace, I still don't like being called sub-human. Human = Japanese, anything outside of that = gaijin.

Moving closer to the subject at hand... In response to Neko kenshi
At all of the dojos I have visited/practice at, I have never been denied the chance to practice simply because I am not Japanese. In fact the Japanese usually won't outright exclude you, they just make being around extremely tough so you quit on your own accord. I have only practiced at one dojo where I was made to feel like an outsider(which is why I don't practice there anymore).
If you can't speak Japanese well that may be another story. They may feel it's a waist of time and not want to be bothered.