Oh geez. At a Wednesday afternoon screening of “The Skeleton Twins,” director Craig Johnson said he accidentally took his parents to see “Nymphomaniac: Volume 1,” the sexually explicit Lars Von Trier drama.

How did that happen? “Nymphomaniac” was last night’s “secret” Sundance feature at the Egyptian Theater. Although most people at the festival correctly speculated that it would be the film shown, Johnson never got the memo. “I thought this is great, it’s my parents’ last night in town,” Johnson recalled in his pre-screening remarks. “Maybe it’s the new Wes Anderson movie — my mom will like that!”

Then Sundance director John Cooper took the stage and unveiled the selection as “Nymphomaniac.”

“For those of you that don’t know,” Johnson explained, “that’s the movie with real sex and penetration.” He asked his mom to leave, but she said she wanted to say.

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“There’s no fucking way I’m watching ‘Nymphomaniac’ with my parents!” Johnson riffed, to a huge laugh from the crowd. He said he climbed over a few seats, so at least there would be a barricade between him and them.

“Thank you Sundance for the single weirdest movie experience of my life,” he added.

“The Skeleton Twins” tells the story of a brother and sister (played by Kristen Wiig and Bill Hader) who reunite after a suicide attempt. The dramedy was purchased by Lionsgate and Roadside Attractions on Tuesday, and it features dramatic turns from Wiig and Hader. “They wanted to do material like this,” Johnson said after the screening. “At the core, they are actors.”