Credit: Kevin Mazur/TCA 2011/

Ashton's gone klepto!

At Sunday's Teen Choice Awards, Ashton Kutcher couldn't help but Punk the show's producers.

The actor and brand-new star of Two and a Half Men showed up in a beyond-casual look for the bash, held at the Gibson Amphitheater in Universal City, Calif. Kutcher, 33, sported long, shaggy hair, beard, straw hat and flip-flops -- and when he won an award of his own, he led the audience in a sing-along of Katy Perry's "Teenage Dream."

The antics didn't stop there. After chatting briefly with Us Weekly (the first day of shooting Two and a Half Men was "fantastic" and "great," he told Us), Demi Moore's hubby made a break for it -- stealing a surfboard prop!

(Although Kutcher won a surfboard award, he had pilfered a prop that the show's crew needed for the rest of the broadcast.) Kutcher was last spotted walking to his car with the board and driving off. The crew scrambled to find a makeshift replacement.