Nico Nico Ni

It is a typical phrase of one of the characters of the animated series "Love Live", its original meaning is "Nico Smile" a song inherited from his father.

This phrase became famous to the "Nico" (character that says the phrase) to become an icon "Cancer" in Internet, and defining to the Weebs

It really does not have a use, it is more considered as a form of "meme"