A line from the song Milkshake by Kelis. (The song was remade by Goodnight Nurse, who made it considerably better and funnier.) Basically, the "milkshake" stands for the woman's sex appeal. When she says, "My milkshake brings all the boys to the yard," it means she attracts all the guys in the area just by appearing there.
Girl 1: My milkshake brings all the boys to the yard!
Guy 1: *to Girl 2* It's better than yours.
Girl 1: *to Girl 2* Damn right, it's better than yours. I could teach you, but I'd have to charge.