Chris Hemsworth's Half-Naked 'Vacation' Cameo Has Ed Helms & Christina Applegate Talking: "Everyone's Mouthes Were Agape"

2015's reboot of National Lampoon's Vacation has laugh-out-loud moments, moments to make you cringe — like the moment the Griswolds' find themselves bathing in sewage — and one exceptionally swoon-worthy cameo. When Thor's Chris Hemsworth stepped on set of the Ed Helms-starring film, co-star Christina Applegate had no clue who he was. "Honestly — and I'm so sorry Chris — but I wasn't familiar with Chris' work. So I was like 'OK, he played Thor, fabulous.' But I'd never seen it," the 43-year-old actress says.

In the film, Rusty Griswold (Helms) is all grown up, and taking his wife Debbie (Applegate) and their two children on a family road trip to Walley World. But they make a stop on the way there, and audiences are gifted Hemsworth's character, complete with weather-man hair and a Texas cowboy accent. "Rusty and his wife Debbie are visiting Audrey Griswold, and she is married to an incredibly hunky cowboy played by Chris Hemsworth," Helms explains. "His name is Stone Crandall. So we're staying at their house, and we're settling down to go to bed, and Stone comes in wearing nothing but very tight underwear. We can see through his underwear that he has an enormous package. We're stunned by this. He is also weirdly oblivious and arrogant about it, and just sort of talks nonchalantly for a few minutes and leaves, and we're left bewildered."

It's a scene that will surely be engrained in audiences' minds long after they leave the theater, but Helms wasn't sure it would ever come to fruition. "I was surprised that he did it. I don't think I would have done it," the Office alum says, admitting: "We were all on set laughing about it and checking it out."

And even though Applegate was unfamiliar with the actor, she was nonetheless approving. "When someone can make me laugh and is really good at their job, I'm really impressed," she says. "I was like, 'He's this funny Australian dude who's really good at accents and game for everything.'"

But nothing could prepare the Anchorman actress for seeing Hemsworth — barely-clad — in their bedroom scene. "We had all been standing at the bottom of the stairs after he had been doing fittings upstairs. Should it go to the right? Should it go to the left? Should it be longer? Should it be shorter? Finally they narrowed in on the hero penis," she explains. "Then we saw his abs, and there was a bit of silence in the air."

The scene features a notably taken-aback Debbie, as she attempts not to stare at Hemsworth's large appendage. "We were all just so damn impressed at how a body can look like that. Like what exercise does one do to sculpt out the abdominal area in such a way?" she asks. "It is unique to anything I've ever seen before except for the [statue of] David. Men, women, children... everyone's mouthes were agape."

See Hemsworth's impressive physique, and so much more, when Vacation hits theaters July 29.

Images: Warner Bros.