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.
October 10, 2007