Timeless derogatory surfing term, generally applied to rank beginners, but also used for any surfer thought to be in violation of surfing's complex unwritten code of conduct; a world champion paddling out to a surf break for the first time and dropping in on a local, for example, would be shouted down as a "kook."

The word "kook" is not a surfy adaptation of "cuckoo" or "kooky," but a play on the Hawaiian word "kukae," which means "shit." According to World War II-era surfer Dorian Paskowitz, there was a small arroyo in the sandstone cliffs at San Onofre where he and his friends would relieve themselves. They called it Kukae Canyon. From there, they began to say that had to "take a kook," and it was a short step, as Paskowitz later recalled to that that "anything bad was a 'kook,' including somebody who couldn't surf—or if he was just an asshole."

The surf leash is sometimes referred to as "kook cord"; in 1987, a California surfing novelty company developed Kook Repellent, an aerosol "silly string" knockoff. "Kook" is one of a select few genre words—"stoked" is another—to remain in usage through the decades. Occasionally spelled "kuk."

A hapless surfing cartoon character named William Kookmeyer was a regular feature in Surfer magazine for 20 years, starting in the mid-1980s. An oddly articulated bronze statue of a surfer, installed off Highway 101 in Encinitas in 2007, was quickly nicknamed "The Cardiff Kook," and dressed (often cross-dressed) under cover of night by local surfers.

Kook: What Surfing Taught Me About Love, Life, and Catching the Perfect Wave, a memoir by Outside magazine writer Peter Heller, was published in 2010. Kook Paradise, a mocking film shot in a 1960s sports documentary style, won Best Short Film at the 2012 New York Surf Film Festival.