Not long ago, Dave Franco was just an A-list actor's D-list little brother, being bullied in a 2008 Funny or Die video called "Acting With James Franco." Dave wanted to act, too, but he was stuck in the big, weird shadow of James, who was balancing high-profile roles with poetry, nudity and crazy art films. Onscreen, Dave's good looks got him typecast as a clean-cut prick. He played "Greg the Soccer Player" in 2007's Superbad and a couple of forgettable bit parts on TV's Greek and Privileged. "I wasn't proud of the projects I was involved in," says Dave, 29. "I didn't want my family and friends to see these things."
Then Dave told Christopher Mintz-Plasse (a.k.a. McLovin' from Superbad) how badly he wanted to fuck him. "You're so hot," Dave said in their first Funny or Die video. "I want to literally cover every single inch of your body with my tongue."
Their stupid-hysterical "You're So Hot" videos went viral and relaunched Franco's career as a lowbrow comic actor. "I found out later that the videos helped me get cast in 21 Jump Street," he says.
Now Franco is a legit rising comedy star. His best work yet came in this summer's smash Neighbors, a frat-house comedy he says "was perfectly catered to my wheelhouse: dick-oriented humor." Franco's shot-slamming frat boy is a jackass, but a jackass with soul – self-aware enough to realize all the partying is temporary, sensitive enough to be hurt when his bud (Zac Efron) turns against him. "After 21 Jump Street, I was offered every douchebag-asshole role in Hollywood," he says. In Neighbors, "It would have been easy to make the frat brothers douche assholes, but we tried to make them human."
Of course, Franco is not about to clean his act up. In 22 Jump Street, out now, he has a cameo as Rob Riggle's prison bitch – and he promises more Funny or Die shorts are on the way. Franco will also reportedly star in The Disaster Artist, a behind-the-scenes romp (directed by James) through Tommy Wiseau's hysterically incompetent cult classic The Room, and he's developing a film based on the novel The Intern's Handbook, in which he would play a hero who is hardly a jerk at all. "To be completely candid, I'm not an asshole," he says. "I swear! I am not a douchebag."
Franco is on a roll, but there's one thing that he just can't wrap his head around: his brother. "I've got no explanation," he says. "I know to expect anything at this point, and I'm still shocked by certain things he does. And I know better than to ask him why he's posting naked selfies."
This story is from the July 3rd-17th, 2014 issue of Rolling Stone.