More than 15 years ago, Joaquin Phoenix was responsible for one of the internet’s earliest viral moments when he appeared on The Late Show with David Letterman in character.

The Oscar winner recently recounted his “horrible” Feb. 11, 2009 appearance on the talk show, which came after he did the pre-interview in character for his Casey Affleck-helmed mockumentary I’m Still Here (2010), which saw Phoenix quitting acting to pursue a hip-hop career.

“I realized that it was just a little silly, so I called them back and I said, ‘Listen, this is what I’m doing. I’m coming out here and I’m doing this whole thing,'” he explained on The Late Show with Stephen Colbert.

“‘And I just want Dave to like, lacerate me. I just want it to be really dangerous,'” Phoenix continued. “That was the kind of intention… I just always wanted to get this reaction and see how I would respond to that. So it was beneficial for no one to know, except when needed.”

Although he recalled the interview was “horrible,” Phoenix noted, “It was strange because in some ways, it was a success, and it was also just one of the worst nights of my life.”

The Eddington actor said the appearance “was so uncomfortable,” adding: “I regret it. I’ll never do it again. I’m so sorry.”

I’m Still Here grossed $626,396 worldwide and holds a 53% Tomatometer score on Rotten Tomatoes, panned as “disturbing” and “painful to watch.”

Following the film, Affleck settled lawsuits brought by producer Amanda White and director of photography Magdalena Gorka, alleging sexual harassment, infliction of emotional distress and breach of oral contract.