Oh, one other thing I'd like to point out, because English isn't a Japanese person's first language, they don't know quite how to use it like we do. Rarely do they hear(see) real-life English, just situations in textbooks, or taught by a non-native speaker of English. What may come off as rude to us, might just be what they think is acceptable.
Japanese is also a very descriptive language, and when translating into English it's hard to make substitutions, same as English > Japanese. So just consider that too, what's rude to us, might not be to them.
It reminds me about when you "/check" someone. It's almost always considered rude to check someone without asking, but Japanese players have become more relaxed about it over time. I still don't know why exactly it's rude, but it's probably like in real life, it's not polite to stare. I've made a point to some of my Japanese friends to explain why most English players don't think "/check"ing is rude, because you're not given the option to accept or refuse a check like you would a trade or party invite, it just happens.
Oh, and thanks Pseulen for agreeing with me. ^^
Though my ex-boyfriend is Korean(adopted) he's a bit raciest.