Perhaps Tatum O’Neal should've tried this excuse: the drugs weren't hers.

That's what Seth Rogen and James Franco are saying about last night's MTV Movie Awards stint where they smoked (fake?) weed on stage.

According to Franco, they were just holding … for MTV.

Backstage, Franco told The Associated Press that MTV put them up to the joke, even supplying the script, the fake marijuana and the fake joint — then had a last-second change of heart about the bit.

"MTV wrote it! … Then backstage there was this big commotion: 'You guys can't say that,'" Franco said. "It says right in the script: 'Lights fake joint.'"

He liked the bit, saying: "that was the joke, because the No. 1 question we get about 'Pineapple Express' is, 'What kind of research did you guys do?'"

Franco said he was disappointed that the cameras went wide.

"I think they killed the joke," he said.

So what was really in the bag?

"I don't know! MTV gave it to us." [AP]