Used to refer to people who have small dicks, it is also a nickname you call anyone. On the other hand females have microscopic nubs, because they don't have a nub. If you are trying to tell someone they have a big dick then you would call them a Bige
You are such a nub.
Stop being a nub.
You little tiny nub.
Can I please suck on your mothers nub?
Wow look at that little nub.