When somebody does something crazy or something wrong that they aren't aware they've done.
Mom: Boy, what'd you wit them Cold cuts in the fridge
Son: nuthin mom daddy threw em out, he said they was no good
Mom: well ya father dizzy as hell, them cold cuts was good for another three days, Ima have to talk to his ass.
1) something/someone thats boring or irrelevant
2) something/someone you could care less about
3) something that's a waste of time
Ex.
1. Dom: how was the midterm?
Manny: it was a dub, they shoulda just did regular class.
2. Dom: do you remember what the morning announcements said about the assembly?
Manny: the morning announcements are a dub, I rarely pay attention to them
3. Dom: what's up with that kid Jean?
Manny: he's a dub, I don't talk to him