When an actor builds his reputation on being a jackass, he’s got to expect young upstarts waiting for the opportunity to pile on.

And that’s what happened to Johnny Knoxville when he shot a promo and showed a screening for his new film, “Bad Grandpa,” at a University of Arizona frat house last month according to several media sources.

Knoxville, 42, star of the “Jackass” movies, was at an unidentified Tucson frat in early September dressed as his alter ego from his new movie, “Bad Grandpa.” Several photos he posted to his Twitter account show Knoxville partying with students.

Later that night, however, someone at the party put Ecstasy in his beer, he told TMZ.

“Someone dosed me with Ecstasy and after that the wheels fell off,” he said. “I wasn’t mad at all. I hadn’t done it since my 20s. I thought, ‘This is awesome!’ ”

Articles in The Mirror and The Sun newspapers in the United Kingdom confirm the story.

“About 30 minutes into the screening, my heart starts racing and I'm like, ‘I am X-ing right now, someone dosed me,’ the papers reported.

"For the rest of the shoot I was just a train wreck and we got a lot of funny stuff. But at some point I ruptured the tendon in my finger either busting through a table or climbing up a net."