Kieran Culkin admits to getting actors high on stage in 'stupid' prank that Mark Ruffalo described as 'the worst thing he ever did'

Kieran Culkin has admitted to getting actors high on stage in what fellow movie star Mark Ruffalo described as 'the worst thing he ever did'.

Culkin and Ruffalo worked alongside each other on the opening night of the 2000 production play The Moment When, where a real joint of marijuana caused some problems.

Culkin, who was 17 at the time, decided to swap a prop joint for real-life marijuana, which ended up getting Ruffalo high.

Mark Ruffalo was left stoned (Monica Schipper/Getty Images)

Speaking in a recent interview with the Guardian, Culkin admitted to being '17 and stupid'.

"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," Culkin told the outlet.

"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.'"

As you'd probably expect, not everyone was impressed with the out there stunt, especially the people in charge.

Culkin recalled: "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.'"

While he may have been a little immature back then, Culkin joked years later about repeating the gaff with Colin Hanks.

"Are you f***ing kidding me? If you ever do something like that, I swear to God, I’m going to punch you in the face," Hanks reportedly said back to Culkin.

Kieran Culkin has admitted to getting actors high (Jo Hale/Getty Images)

Culkin added to the Guardian: "But then towards the end of the run, I said it again and he shrugged like he was saying, 'If you do, it might be fun.' The thing is, his character has to roll the joint every night on stage. So, one day I hand him the real pot on stage and I see him, like, react. It looked like he was excited.

"But then he got too excited and got nervous. And his hands started shaking so much that he couldn’t get the joint rolled, and when he tried to light it, it fell apart. Thankfully, we had a pre-rolled fake joint behind him, so we ended up with that."

Funnily enough, Ruffalo has spoken about his weed experience previously on BBC's The Graham Norton Show.

The actor spoke about how he smoked a 'giant blunt' with one of his co-stars, while admitting his fellow star had never smoked before.