You might have expected Slash's favorite moment of debauchery to have taken place somewhere out on the road with Guns N' Roses during the hedonistic '80s. Instead, the guitarist says his most memorable tryst happened when he was barely a teenager.

Slash tells TMZ (video embedded above) that he and a girlfriend once had sex while her mother slept on a nearby couch -- and that he was all of 13 or 14 years old at the time. But that's not all. Worried that mom might awaken at the sound, Slash adds with a laugh: "We doped her [with] Halcion."

Halcion is a sedative prescribed for severe insomnia.

Slash remains unrepentant about the incident, years later -- saying it's "human nature" for people to be interested in pushing the sexual envelope. It all depends, he adds, "on whether you're gonna get busted or not. ... If you're gonna get arrested, I would zip up and get the f-- out." Otherwise, Slash concludes, "There's no ridiculous place, if you can get away with it."

So, look out Las Vegas! Slash continues his tour with Aerosmith tonight in Sin City. They then head to California, Colorado and Texas as August unfolds. The Let Rock Rule concerts conclude in September.