Can't resist doing a limerick with this one, Dgeigh. Words like "Nerts!" don't come along every day. :)

A very useful word is "Nerts!"
Which a cruciverbalist inserts
In a crossword puzzle -
Our wits to muzzle.
"Nerts! This crossword really hurts!"

MSN Encarta: nerts [ nurts ]

interjection

expression of contempt or refusal: a word used to express contempt, disgust, or refusal (dated slang)

[Mid-20th century. Alteration of nuts.]