An exclamation, usually mean spirited, that implies someone has made a
mistake or misfortune has befell them.
Usually, it is used as a means to 'kick someone while they are down'
Buns can also be substituted for certain other slang terms. For example, a
person can say "my buns" implying the same thing as "my bad."
The term
first became widely used in the New York area and has since spread west.