bang nanny
A woman that a man gets into a relationship with primarily so she'll watch his kids from another relationship
Her: "Sorry, we have to cancel girls night. I forgot that Boyfriend has custody of his kids tonight and so I have to make them dinner, help them with their homework, and prepare their school lunch for tomorrow."
Friend: "Girl, he's using you as a bang nanny! DTMFA."
Friend: "Girl, he's using you as a bang nanny! DTMFA."