Beloved funnyman Fred Willard was reportedly arrested for pulling a Pee-wee Herman at a Los Angeles adult movie theater last night.

According to law enforcement sources, LAPD undercover vice officers went into the Tiki Theater in Hollywood and found the 72-year-old "Anchorman" star watching last night's feature ... with his penis exposed and in his hand.

We're told Willard was arrested around 8:45PM and booked for lewd conduct.

It was a quick release -- we're told he was out of police custody a short while later.

Willard is best known for his great work in “Best in Show” and "Anchorman” – and now maybe for his persistent libido.