Nothing Special, basically if something isn't even worth telling.
!!don't confound it with Nationalsozialismus!!
NS is often used by younger people all around the world who think, what you've told them isn't interesting or isn't anything they wouldn't do.
It's the short version of "nothing special".
A: "hey dude, yesterday I crashed my parents car into my grandpa's house"
B: " dude that's ns, I did that with a plane last week"
A:"well, I guess you are just better than me"
B: "guessed right!"