What was the saying Don't be a cotton head ninny muggin?

"Don't be a cotton-headed ninny muggins" is a humorous phrase from the holiday movie "Elf," spoken by the character Buddy. It playfully suggests that someone is being foolish or silly, comparing them to a whimsical character with a childlike demeanor. The phrase has since become a popular quote, often used to lightheartedly admonish someone for their antics. Overall, it embodies the film's spirit of fun and innocence.