Guess Which Culkin Brother Admits To Getting Mark Ruffalo High On Stage

While method acting isn’t exactly his style, one Culkin brother proved there’s no substitute for authenticity—especially when it comes to stage props.

In a resurfaced 2012 interview, Mark Ruffalo shared a wild story about a "naughty young actor" who swapped a fake stage joint for the real thing during a live performance, leaving him unexpectedly high in front of an audience.

Now, years later, one of the Culkin siblings has finally stepped forward to admit they were the mastermind behind the prank.

Kieran Culkin made his acting debut alongside his brother Macaulay Culkin in the iconic 1990 holiday film "Home Alone," playing the role of Kevin McCallister's mischievous cousin, Fuller. He reprised this role in "Home Alone 2: Lost in New York." Shortly after his Hollywood debut, he appeared in Playwrights Horizons‘ 2000 production of James Lapine‘s "The Moment When," alongside Mark Ruffalo.

With a stash of prop joints backstage, Culkin couldn’t resist the temptation to swap one out. “Uh-oh. I believe it’s happened,” he thought to himself weeks later as he caught a familiar scent and “just watched” Ruffalo take a hit before passing it to their co-star.

During intermission, Culkin felt compelled to confess. “I’m like, ‘I thought this was a good prank. I’m stupid. Oh my God, I’m so sorry,’” he told The Guardian. “But actually, they loved it. 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.’”

Culkin went on, “Then the stage manager comes stomping in and goes, ‘I don’t care whose it is, or what happened, but Kieran, give me the joint.’ Sheepishly, he handed over the remains. “She said, ‘Ruin your life on your own time.’”

The Golden Globe winner seems to have taken the experience to heart. “I was 17 and stupid ... I was young. I’m 42 now. I know better. I’m not going to try to get anyone high on stage,” he said.

Mark Ruffalo first shared the hilarious backstage mishap during a 2012 appearance on "The Graham Norton Show."

“There was a play that I did that I had to smoke a joint in the first scene," he said at the time. "And of course, there was a very naughty young actor I was in the play with, who on the opening night with all the critics, he slipped a real joint onto the prop table.”

Known for fully committing to his performances, Ruffalo admitted, “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 said, miming an exaggerated inhale. “Between the two of us, we smoked a giant blunt on stage.”

As the scene played out, Ruffalo recalled feeling unstoppable. “And I’m like, ‘Man, I am in it tonight. I feel it. I’m on fire. I’m feeling it… why’s that dude standing backstage laughing at me?’” That’s when he realized the young actor responsible was standing offstage, cracking up. “And I just went, ‘Oh sh-t.’”

But the story has a silver lining. Ruffalo added with a grin, “But at the end of the play, I got the best reviews of my entire career.”

Kieran Culkin skyrocketed to global fame with his role as Roman Roy on HBO's critically acclaimed series "Succession." Playing the sharp-tongued, irreverent youngest son of media mogul Logan Roy, Kieran became a fan favorite for his biting humor and vulnerable portrayal of a deeply flawed character. His performance earned him multiple Emmy and Golden Globe nominations, and he took home a Golden Globe Award for Best Supporting Actor in a Series in 2024.

Kieran Culkin has firmly established himself as one of Hollywood’s most versatile and compelling actors, proving time and again that he’s much more than just “Macaulay’s little brother.”