What you call a friend in IM, text message, or in regular conversation who has knowledge of leet speak, and uses it frequently. Can be used as a friendly topic ender or a profane interjection, both equally friendly. Also can be used against a third party who you think sucks and deserves to be called something that fits their idiotic behavior or disposition.
Bro 1: "aight nigz0r I'll talk to you then."
Bro 2: "peace braski."
Idiot: "lololololol iz sooo kewl! iz a total pwnz0r! I camp your base and fuck men!"
Me: "Damn right you do!" -shoots in the face- "Nigz0r!!!"