Josh Kloss aired his allegation on Instagram where he recalled his early interactions with Perry, who was "cool and kind" but when other people were around she was "cold as ice".
He says he took a friend to meet her at a birthday party and as he turned to introduce that friend, Perry "pulled my Adidas sweats and underwear out as far as she could to show a couple of her guy friends and the crowd around us, my penis".
"Can you imagine how pathetic and embarrassed I felt?" he wrote.
Kloss says he was told by her reps to keep things under wraps and even edited his answers in interviews.
He then published what he claimed was a screenshot of communications between himself and Perry's team, writing, "I was supposed to minimise myself and stay PC to protect her 'image.' I listened and was a good boy. The fear sticks with you when you are censored to protect someone else's image.
"But in return [you're] treated like a prostitute and exposed in front of a group of her friends and other random people. Then you are shocked and you block it out because you watch the face of children being uplifted by positive music she sang. And your mind is stuck trying to do your job and protect her bs image or be honest and help the global dialogue about power and abuse."
Last year Perry was accused of "forcibly kissing" an American Idol contestant, and the year before she was accused of grabbing then-17-year-old singer Shawn Mendes' buttocks without his consent.
