NEW YORK (AP) ― Shooting a love scene with Charlize Theron would be a dream come true for many actors, but for Patton Oswalt, who co-stars with the Oscar-winning actress in the new movie “Young Adult,’’ the experience was “a nightmare.’’

“Why do I have to be in my underwear next to the most physically perfect person on the planet? Why couldn’t I have been next to John Goodman or Michael Moore in their underwear?’’ said Oswalt at the film’s premiere Thursday night. “It was a dream that turned into a nightmare.’’

The comic drama, which opened in select cities Friday, stars Theron as Mavis Gary, a boozing, delusional author of young-adult novels who returns to her hometown to win back her happily married high-school sweetheart, played by Patrick Wilson.

Mavis forms an unlikely bond with nerdy former classmate Matt Freehauf, played by Oswalt.

Oswalt said he kept a souvenir from his time on the set with Theron ― post-traumatic stress disorder.

“Every time I hear a car backfire, I think I’m getting naked again,’’ he joked.

The film, directed by Jason Reitman and written by Diablo Cody, goes into wide release on Dec. 16.