Matt Damon had to pull his swimming trunks up his butt to get an effective tan for his latest film
The 42-year-old actor went through the pain barrier while spray tanning for new biopic 'Behind The Candelabra' - in which he portrays Scott Thorson, gay lover of late US pianist Liberace (Michael Douglas).
He is quoted by The Sun newspaper as saying: "With the spray tanning, the Speedos were actually much smaller than the bikini underwear they gave me when I got the tan.
"So I had to pull the underwear up the crack of my butt to give myself a Brazilian tan.
"It's like getting covered in maple syrup - it's really gross."
The tan also surprised Matt's wife, Luciana Bozán Barroso, who was concerned about his rear.
He added: "Afterwards my wife was like, 'What the f**k has happened to your ass?' "
Despite the discomfort he faced, Matt was pleased with the results after a scene he suggested to director Steven Soderbergh - in which his bare bottom was exposed - was included in the movie.
He said: "I explained to [Steven] in this parking lot in West Hollywood about my Brazilian tan line that I had to get to make some of the outfits fit and not show a tan line.
"Steven sat there listening and I said, 'It would be really great - it's the wrongest thing you've ever seen, but what if by the end of the thing I drop the robe and get into bed and you see the Brazilian tan line?' And Steven just looked at me for a long time and said, 'Oh, I know where to put the camera.'
"So I'm really proud of that scene cause it's thrown away. And my behind is very large in the frame but it's out of focus cause the focus was thrown deep to Michael."