If you're one of the moviegoers who helped propel his most recent film to $84,517,957 in worldwide box office earnings, you already knew that skateboarder and reality show star Bam Margera is a Jackass. But what you might not know is that his most dangerous stunt involves having sex with his fiancée while driving.

In an appearance on Howard Stern's Sirius Satellite Radio show this morning, the Jackass and his betrothed, Missy Rothstein, shared their secret for keeping their relationship fresh. "I figured out a way to hump while I'm driving!" Margera enthused. "I'll just be like, 'Let's just bang out right now!'... I live in the woods, man, so I can drive all over the place. It's way better than the bed."

"I'm facing the road," said Rothstein. "But the seats in the Hummer are nice and wide...."

"Maybe there should be a disclaimer on this," Stern co-host Robin Quivers suggested.

Margera and Rothstein were on the show to promote their new MTV reality series, Bam's Unholy Union, which the New York Times described this weekend as chronicling "the unorthodox, mostly unscripted preparations for Mr. Margera and Ms. Rothstein's wedding." (Margera, who lives in West Chester, Pennsylvania, says the wedding will be attended by all the Jackasses, plus one: friend Jared Leto.)

As with any reality series, the producers appear to have sexed it up—literally. Margera, who's been romantically linked to that other bright star of MTV, Jessica Simpson, also told Stern about his debauched Las Vegas bachelor party in a hotel room featuring a bowling alley and "lesbians eating each other out." When asked where the performers came from, Margera answered, "MTV rigged it for me!"

Of course, as befits a Jackass, someone got hit in the groin by a bowling ball.

Photos: MTV