AP Photo/Chris Pizzello

Sean Penn wants you to party.

Sort of. The guy who brought Fast Times at Ridgemont High's stellar stoner Jeff Spicoli to life appeared at the Coachella music festival to inspire more people to get involved in political and environmental causes, including his own cross-country biodiesel caravan.

"The real powerful third party," he told the audience, "is you and me."

For more partying at the Coachella festival, check out our gallery and Hollywood Party Girl's report.