This slang has been in use since 1986! Even high school teachers use it now. Doubt it came from the ghetto as most of them don't know the word disrespect. It probably came from college students. Anyway you had better get used to this word because they will be dropping it off the slang list soon. If a slang word is not offensive and in use long enough it becomes part of the language.
Figures. What with the public schools being SO good, huh?
Actually the odds are that the word "diss" did originate in the ghetto. One thing that blacks regularly talk about, and this includes black athletes, is respect. I've many times heard black gang members explain that they had shot a person because "he disrespected me".