[eequah9L]

I don't think it's anything "reasonable". Like, OK, there might be objective reasons why you need to clarify which technical term you mean by a word that has multiple meanings in your native language, and use (typically) English to clear it up.

But I think most of the time it's just seen as hip, interesting, an extra flavor (flavour?). I do this occasionally -- sprinkle a foreign phrase here and there in my native Czech when I see that it fits and the other party might get it. More if I'm drunk. Some of my friends do it as well, in some social settings a number of jokes could be foreign language references. On the other hand, some people find it infuriating, as you note.