Promoting the upcoming film adaptation of the book, the bass player has been asked about the most controversial story and now insists he may have made it up.
"I was outta my head and it's possibly greatly embellished," Nikki tells Rolling Stone, apologising for even suggesting he was involved in a rape situation: "Those words were irresponsible on my part," he adds. "I am sorry."
The story in the Motley Crue book, which the band wrote with author Neil Strauss, suggests he may have participated in a sexual assault at a party.
Sixx told the writer a woman he knew pulled him into a small room and the two began having sex. He later returned with bandmate Tommy Lee and tricked the woman into thinking the drummer was him.
"We f**ked for a while, then I told her I had to go to the bathroom. I went into the party and found Tommy," Sixx recounted for the book. "(I said), 'Dude, come here'. I grabbed him (and said), 'I got this chick in the closet. Follow me, and don't say a word. When I tell you, start f**king her'."
"In the closet, I stood directly behind Tommy. He f**ked her while she grabbed my hair and yelled, 'Oh, Nikki! Nikki!'"
Sixx said he completely forgot about the tryst until the woman called him the following morning and told him she had been raped, explaining a man had assaulted her as she hitchhiked home from the party.
In the book, Sixx said the story made him realise he had "probably gone too far", adding, "At first, I was relieved, because it meant I hadn't raped her. But the more I thought about it, the more I realised that I pretty much had. I was in a zone, though, and in that zone, consequences did not exist. Besides, I was capable of sinking even lower than that."
In his statement to Rolling Stone, Sixx insisted he had no memory of the story because the interviews for the book took place during a "low point" in his life, when he was drinking heavily and abusing drugs to deal with a failing romance: "I honestly don't recall a lot of the interviews with Neil," he said.
"I went into rehab in 2001 and really wish I would've done my interviews after I was clean and sober, like I am today... There is a lot of horrible behavior in the book. What I can tell you is that we all lived to regret a lot and learned from it. We own up to all our behavior that hurt ourselves, our families, friends and any innocents around us."