Ashton Kutcher's former Punk'd cohort, Dax Shepard, makes his big-screen acting debut in the new comedy Without a Paddle (opening Aug. 20). He plays Tom, a lovable boozer and pothead with a tendency toward dishonesty. Sounds like a piece of cake for Dax, right? Actually, the 29-year-old UCLA grad (who majored in anthropology) insists his doofy slacker role really was a stretch.

"In Paddle, I play a guy who is compensating for not having an education," Shepard explains. "I think of my character as someone who is as intelligent as Dan [Seth Green's character], but Dan had good parents and went to medical school and became a doctor, and Tom just went to jail. So he's trying to make up for the fact that he knows nothing, and feel smart by lying a lot and trying to be an expert at something."

How did Shepard make his jump from bookworm to MTV prankster in real life? "I actually made the transition from acting to anthropology and then back to acting," he says. "Basically, my mom would pay my rent while I was a struggling actor if I went to college. So it was my job to go to UCLA."

Sounds like a sweet gig that's paid off, even if Shepard plans to continue dumbing himself down in movies. In addition to Paddle, he just wrapped an as-yet-untitled film by Beavis and Butt-head creator Mike Judge. "It is a hilarious movie," he previews. "Luke Wilson gets frozen in time for 500 years. When he wakes up, only the idiots have reproduced. Which is not far from what is happening. I play maybe the biggest idiot in the future. I'm his best friend and lawyer."

Shepard was clearly thrilled to work with Judge, who's also the man behind Fox's King of the Hill and 1999's Office Space. "I'm head over heels in love with Mike Judge," he admits. "He's the smartest closet genius. I mean, he was a physicist before he was a cartoonist. He knows everything about everything, and he's just kind and the most humble guy.

"[As] a testament to how smart he is," he continues, "by saying everyone is stupid in the future, you can actually make s--- look like it [did in] the past because everything got so crappy. It is a great get-out-of-jail free card for a low-budget futuristic movie."