Greetings.
I have absolutely no idea if this is appropriate for Doper input and discussion, nor how naive this question is since I live in a cave with a television feed and phone line, plus two cats (Weirddave, the cats have come out from my brother’s closet, now). So…edit away…
What I am interested in knowing is whether someone can help me track the rise in popularity of this expression. Was there a particular artist, medium or social/cultural group that originated use of this expression, how long, how has it crossed over, etc.
I can’t think of any question more appropriate for the Straight Dope. The origin of the term seems rather obscure. The OED says its earliest citation for the term is 1991: http://www.oed.com/public/readers/list_frame.htm (unfortunately they don’t say where). This site suggests that its origins lie urban prostitution culture and that it may have mutated from the terms “pimp arm” and “pimp slap.”
i always thought it arose from pimp culture, and spread.
jb
What about popular or gangster rap, theyve given many great slang terms.
DrLao,
I shouda known you’d have a decent answer.
Cool! 
So…does anyone have a musical cite that dates this?
Thanks, katerinatoo. I actually found what the OED is talking about, I think. 1991’s Guns 'N Roses song “You Could Be Mine” contains the line (from http://www.google.com/search?q=bitch+slap+lyrics+1990&sourceid=opera&num=0&ie=utf-8&oe=utf-8):
It is not entirely clear from the context what “bitch slap” means. It is kind of strange nowadays to hear it used as an adjective like this. So, this sounds like it is fairly early in the term’s exposure. Interestingly, this song appeared on the soundtrack to the hugely successful 1991 film Terminator 2: Judgement Day.
"With your bitch slap rappin’
And your cocaine tongue "
I believe that same quote was also used in Appetite for Destruction. Not in a song, but in the liner notes or thank-yous or something. I don’t have a copy here with me to cite though.