Means, Best, Awesome, Super, Sexy, man. Derived from early arabic.
hey, look at that guy. He is so Nish
Retard who try to manipulate others to suck a wiener but only successfull when he meet another similar type of person like, ugly fat guy from midwest.
One guy: "look at that guy, he looks like a complete idiot"
Other Guy: "yeah, he is so Seibel"