An abbreviation for; You Big Nut.
Noun,
Slang.
1. A term used to describe someone who is
clumsy, off-kilter, or somewhat foolish.
On their way to
lunch...
Mr. Valentine: Mr. Malchow, I think I forgot my
wallet at the
office.
Mr. Malchow: Well, why'd you do that YBN?
Mr. Valentine: Because I'm a big nut.