the worse thing you can say to someone is your mother is a whore.. your momma is just a shortened version
He said it was obscene so I figure it was an allegation about something his mother did.
The worst thing we would say was your mother wears combat boots and she dresses you funny.
Growing up in the 50s the worst thing I ever heard was "Your mother wears army shoes!" Nowadays that is so common that most people would not take it as a pejorative remark.
Regards,
GtG