A girl who has macaroni and cheese nipples has abnormally long nipples and is lactating. The milk excreted from the nip dries around the end and oozes out uncontrollably, thus looking like day old macaroni and cheese.
Dan: "Dude does courtney have macaroni stuck on her chest?"
Gil:"No dude i think shes lactating. She has an extreme case of macaroni and cheese nipples."