One can say (post) the word Japanese, but not the shortened version, on this site.
Some time ago someone included the shortened version in post that was brought to my attention. I don't remember the specific post, but did agree to censor the shortened version going forward.
I'll admit that even I struggle with this rule a bit. Rode a Honda Interceptor for nearly five years, and loved it, but tend to fall into this conversation on the knock-offs. I used to refer to my old Ducati SS as a Trashy Italian *****, but now say it's one of my previous "Hotties"