Nani in Japanese is a version of "what" it does not necessarily mean what, it has some different variations depending on the sentence structure. So many people lately keep randomly putting it in their memes. In a way this is somewhat racist and quite rude. Just because it is a trend does not mean it is a nice one. Just because it shows up every now and then in anime doesn't make it just a random thing to run around saying. I am not trying to be rude or hate on you, I am just trying to tell you. Please do not hate me, I am just offering advice. I think the meme is funny. Thank you for your time.
~Stevie