I'm guilty of it to an extent in an RP I'm in. My RP partner is actually studying Japanese, and I'm dabbling for now until I get off my lazy butt and see if I can take a few classes at uni. But I tend to confine myself to endearments and respectful forms of address. I use a conlang version of elven with roots in Tolkien's work, originally developed by Tel'Mithrim for roleplaying purposes.
When it comes to my original fiction and fan fiction, however, there's not a word of Japanese. I don't write in an anime fandom, and my original works aren't set anywhere near Japan. I agree that it's utterly silly in so many applications where it's done, and when it's obviously just whatever is spat out of Google Translame... ouch....