The partner of a piss baby. They egg on the piss baby by supporting their piss kink and acting like their mom.
"Jennifer is such a Piss Mommy, she's always acting like her boyfriend's mom."
A person who is looking for a partner to be a mother in a romantic relationship. (Especially if they have a piss kink.)
"Bro, my ex is such a piss baby, he wanted me to clean up after him all the time and piss on him in bed."