UDB1 is a shortened version of You Dumb Bitch!
U = You
D = Dumb
B = Bitch
1 = !
It was found as a capture code on megaupload 11:00 A.M. December 7, 2009.
Woman: Clark. What does UDB1 mean? I just saw it in the comments on my youtube video.
Clark: You Dumb Bitch!
(You get where this conversation is going)