wingnut (n.) Look up wingnut at Dictionary.com
"nut with flared sides for turning with the thumb and forefinger;" so called for its shape. Meaning "weird person" recorded by 1989, probably not from the literal sense but from the secondary sense of nut, influenced perhaps by slang senses of wing in wing-ding "wild party," originally "fit, spasm" (1937). An earlier, British, sense of wingnut was "person with large, protruding ears" (1986).