Knowing random words and phrases here and there and then using them like you know what you're doing kinda pisses me off. Hell, even if you were fluent in Japanese, speaking it to people who don't would still be a dick move. I'm fluent in Spanish, but the only people I use it around are from Mexico
It might be annoying in the beginning, but it really helps people pick up the language. I study Japanese at a university now, but picking up phrases is how I started. I didn't use them around other people, but I did write them down and it helped me get started.
If they do...
*takes out board*