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.
Rufus: It cost me a couple of Jeffersons to smack my bitch up last night, baby, so don't get stingy on me tonight.
The phrase was made famous by The Prodigy. The phrase does not mean to hit your girlfriend, nor does it advocate violence toward women as it literally implies.
"You know it."
"Then smack my bitch up.
smack is slang for the drug heroin.
put them together and you get smack my bitch up, in other words to inject heroin into your main vein in your arm.
also widely known from the famous song smack my bitch up by the prodigy.
The song was coupled with an equally controversial video, which depicts a wild night of sex, drugs, and violence from a first-person perspective. However, it was far from mindless- in fact, the video consistently ranks as one of the best ever made, and contains a twist that makes people rethink their entire interpretation of the song. Personally, I came away from it thinking the song was one big joke making fun of people who will dance to anything without caring what the lyrics are, but I'll let you decide for yourself.
Girl: OMG, that song is so offensive!
Guy #2: Yeah, but you have to admit, there's a lot worse. Just listen to rap music.
In England, where the song originates from, 'smack' is common slang for heroin, although contemporarily can refer to any intoxicant.
Miles: Homes, Smack My Bitch Up.
Also refering to bitch-slapping something to show ones physical prowess over it.