To do something
nice (esp. wonderful) for
one's girlfriend, spouse, ho, etc., especially where the thing done is considered of
high value by the recipient. The saying can be used both literally (as when administering a fix or donating the
dope with which to do so) but is perhaps more often used figuratively (as when doing something considered
nice).
Similar to "smacking oneself up", as in giving oneself a much needed fix, a reward fix, party fix, etc. To "smack up" someone, then---while not necessarily implying a positive motivation for the act---is usually considered a favorable act. And to
smack one's bitch up is considered especially charming and gentlemanly, usually leading to some sort of reciprocity by said bitch.
Bo: Yo,
Jim, I'm gonna smack my bitch up with these flowers and
candy when I get home, so maybe I'll get lucky tonight.
Rufus: It cost me a couple of Jeffersons to smack my bitch up last night, baby, so don't get stingy on me tonight.