Kieran Culkin Admits Swapping Mark Ruffalo's Prop Joint for Real One When He Was 17 in 'Stupid' Prank

In a new interview with The Guardian, the Succession star admitted that he once swapped a prop joint for one with real marijuana when he was cast in a stage production alongside Mark Ruffalo in 2000.

"I was 17 and stupid," Culkin prefaced of his time in Playwright Horizons' production of James Lapine's play The Moment When at the time. "I'm like, 'I thought this was a good prank. I'm stupid. Oh my God, I'm so sorry.'"

"But actually, they loved it," he went on. "Mark says, 'I haven't smoked pot in 10 years. The second half's going to be so much fun.' There was this other actor who had never smoked pot in her life. She goes, 'Is this what being high is? This is lovely.; And then Phyllis Newman comes in and goes, 'I haven't smoked pot since the 1960s. Thank you, darling.'"

He continued, "The stage manager comes stomping in and goes, 'I don't care whose it is, or what happened, but Kieran, give me the joint.' I sheepishly handed her the roach and she said, 'Ruin your life on your own time.'"

Now 42, Culkin says he knows better, and is not going to "try to get anyone high on stage."

While this marked the first time Culkin was fessing up to the incident, Ruffalo previously alluded to the stage snafu during an appearance on The Graham Norton Show, where he kept Culkin's identity under wraps.

"There was a play that I did where I smoked a joint in the first scene. Of course, there was a very naughty young actor I was in the play with," Ruffalo, who admittedly said he tends to "overdo everything," began. "On the opening night with all the critics, we slipped a real joint onto the prop table."

"So, when you're out at a party, you take two puffs and you say, 'Okay, that's enough. I'm so stoned, but I was acting, so I was just like—," he explained, faking a big inhale. "Between the two of us, we smoked a giant blunt onstage."

It all worked out for the 13 Going on 30 alum, who said by the end of the play he "got the best reviews of my entire career."

"But I'd never do that again," Ruffalo quipped.