"We're not actually that much of exhibitionists in front of 18,000 people," Timberlake said on Wednesday's Jimmy Kimmel Live!
But they couldn't control themselves when the "Kiss Me Cam" came out.
"They were playing Sonny & Cher's 'I Got You Babe,'" Timberlake explained. "And we were watching all these sort of elderly people kiss -- it got kind of weird there for a second, I'm not going to lie -- but it was really endearing."
"And then they cut to Dustin Hoffman and his wife, and he planted an open mouth kiss on her that was, like, award-winning in its own way," he continued.
Then, Timberlake said, "they cut to us, and I was not to be undone. So I mounted my girlfriend in front of 18,000 people."
Looking back, "That was one of those moments where I should have made a better decision," he said.
Kimmel agreed: "Keep that in the motel," he cracked.