The phrase "do boy" has been used in the early 90's in southern ebonics to classify a certain type of guy.
A "do boy" is a guy that likes or loves a girl that is not really interested in him, but the girl will keep this guy around to do things for her.
She'll keep him around to wash her car, buy her something to eat, and run errands for her. But she'll NEVER be his GIRLFRIEND, and will only hang out with him when she can't find nothing else better to do.
Girls only have this kind of guy around to boost up their self-esteem so when other relationships go wrong they can always call up the "do boy" to take them out, or tell them how beautiful they are.
I now it's ill but people actually do this.
Kacey: Girl, I didn't know you was dating Marcos.
Tiffany: I ain't dating Marcos, he just my "do boy".