The 'Fury' actor spent five days sitting in a Los Angeles gallery in silence with a paper bag on his head, with members of the public invited to choose an item from a selection on a table and sit with him for a while, and the 28-year-old-actor says one encounter was extremely unpleasant.
He said: "One woman who came with her boyfriend, who was outside the door when this happened, whipped my legs for ten minutes and then stripped my clothing and proceeded to rape me
"There were hundreds of people in line when she walked out with disheveled hair and smudged lipstick. It was no good, not just for me but her man as well."
And the 'Nymphomaniac' star says the experience was particularly "painful" because his girlfriend Mia Goth, 21, was outside waiting to see him - and he couldn't discuss what had happened with her because of the nature of the #IAMSORRY installation.
He added in an email to a Dazed and Confused magazine writer: "On top of that my girl was in line to see me, because it was Valentine's Day and I was living in the gallery for the duration of the event -- we were separated for five days, no communication.
"So it really hurt her as well, as I guess the news of it traveled through the line.
"When she came in she asked for an explanation, and I couldn't speak, so we both sat with this unexplained trauma silently. It was painful."