The 27-year-old plays Christian, who is on the verge of breaking up with his girlfriend, played by Florence Pugh, when she decides to tag along on a trip with him and his group of friends to a Swedish countryside retreat that turns out to be terrifying.
The disturbing movie, directed by Ari Aster, who helmed last year's equally unnerving horror movie Hereditary, features one scene in which Christian is drugged and forced to take part in a twisted mating ritual with one of the villagers.
And it was during this scene that Reynor really pushed for his character to have more on show in an effort to strip his toxic masculinity from him.
The "Detroit" star told Variety: "I was advocating for as much full frontal as possible. I felt like it was really important. When I read the script, I saw an opportunity to take a character who exhibits a lot of archetypal male characteristics - like male toxicity - who has all of the stuff stripped away from him through the course of the film and then ultimately finds himself in this situation which is kind of the ultimate humiliation."
Discussing Aster's input, he continued: "It was always intentional to have the full frontal. That was what Ari wanted to do. But I was really saying, 'We got to do as much of this as possible'."
Reynor was also keen to see the Midsommar with an audience, as he was desperate to see their reaction to the twisted and disturbing scene.
"Half of the audience will burst into laughter. Like a nervous laughter, but laughter nonetheless," the actor said. "And half of them turn around and they're looking at people like, 'What the f**k are these people laughing about?' "
"Midsommar" is in cinemas now.