An expression of total adoration and surrender. Said of a person, object, or situation that you're totally in love with to the point where you'd completely give yourself to, dignity and all. It also implies that the object in question is awesome enough to be worth of dominating you completely.
Dolores: Here comes Brad!
Angela: Goddamn, I love him! I just wanna marry him and be his sweet little bitch!
Tim: Check out that sweet Viper over there!
Bill: Ah, baby! I'd marry that and be its sweet little bitch.
Janet: SPRING BREAK! WOOT!
Craig: Why don't you fuckin' marry it and be its bitch?