This term is a drunken slur of endearment commonly used when a friend is carting your drunk-ass home. Meaning "My brother from another mother."
I promise not to puke on your leather, nubba nubba, thanks for the ride.
Driver: Thanks for not puking in the car, my brother from another mother.
Drunk: no worries, sorry 'bout the hubcaps, nubba nubba.