'I'm Stupid.' The Story Behind That Time Mark Ruffalo Got Pranked Epically By Kieran Culkin, And Pot Was Involved

Kieran Culkin slightly smirking in a red hoodie in A Real Pain.
(Image credit: Searchlight Pictures)

Due to his part in the 2024 movie A Real Pain, actor Kieran Culkin is one of the awards season contestants the world will be following intensely. With a 2025 Golden Globes nomination for Best Performance By A Male Actor In A Supporting Role, the Succession cast alum adds some excitement to what already looks to be a competitive year overall. Which is no surprise, as the mischievous performer once infamously got in trouble for hubbub of a different kind, as he’d pranked co-star Mark Ruffalo with an actual joint on stage.

The story was brought up during an interview with Kieran Culkin and The Guardian, which recalled the incident as happening while he was working with the MCU vet in 2000. Both men were starring in the play The Moment When, and a bag of fake joints presented the then-17 year-old Culkin with an opportunity to sneak a genuine article that was consumed on stage. Which led to the following anecdote:

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. 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.’

The plus side of this interaction is that the future Scott Pilgrim vs. The World cast member would appear to be that his cast mates did not have a problem with this rather method prank. You can kind of imagine Mark Ruffalo walking off stage after the scene in question, delivering one of his trademark laughs of warmth, and making the admission shared above. I don’t know if I really expected anything to the contrary, but it’s still good to have confirmation.

However, it’s still kind of fitting for Kieran Culkin to be telling this story on the press tour for A Real Pain, as that’s probably what the show’s stage manager had secretly named him after this incident. At least, the assumption’s pretty strong, as the other piece of this story saw the party ending thusly:

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. I sheepishly handed her the roach and she said, ‘Ruin your life on your own time.’

Oh 2000 really was a different time when it came to the legal and sociopolitical outlooks on marijuana. You truly had to be there, and Kieran Culkin has the story to prove that he indeed was. One has to wonder if co-star/director Jesse Eisenberg knew about this story before they shared their own scenes of implied drug use in A Real Pain. Which then only turns into a question of whether or not the props used on screen were just props.

Given that Kieran Culkin’s reasons for not showing his kids Home Alone show how he’s become a more mature and concerned man, one could think those days are over. But then again, only those who know Culkin the best, and maybe Mark Ruffalo, would know for sure. While you contemplate that question, don’t forget that you can still catch Kieran Culkin's acclaimed performance in A Real Pain, both in theatrical release and through in-home PVOD rental.

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Mike Reyes
Senior Movies Contributor

Mike Reyes is the Senior Movie Contributor at CinemaBlend, though that title’s more of a guideline really. Passionate about entertainment since grade school, the movies have always held a special place in his life, which explains his current occupation. Mike graduated from Drew University with a Bachelor’s Degree in Political Science, but swore off of running for public office a long time ago. Mike's expertise ranges from James Bond to everything Alita, making for a brilliantly eclectic resume. He fights for the user.