In the S2 finale, I can't remember if she said she could or couldn't remember the night she lost her virginity, but I'm going on the assumption that she couldn't (although I think that it was Adele who couldn't, or maybe Addison just remembered that it was bad…I digress). Song by Mudhoney.

Sweet Young Thing Ain't Sweet No More

Addison can't remember the first time she had sex, but she can remember the first time she had sex with him. She remembered the guilty way she'd slid into the house the next morning, praying that Derek hadn't bothered to come home and had, instead, remained in the on-call room. She prayed he wouldn't notice.

The first time she slept with Mark Sloan, she was drunk and he took advantage. Of course, Mark argued that he was the one plastered and she had, in fact, been the one taking advantage, but she knew better. Or so she believed. Either way, booze was definitely involved.

They had been friends, in a strange, twisted, not really friends sort of way. She was upset that Derek was never home, Mark was upset because that was just how Mark was, and she ran to him because there was no one else willing to do shots of straight vodka with her at five o'clock in the afternoon. She had started crying, the crying had led to the drinking, the drinking to the talking, and then she couldn't quite bridge the gap from being harmlessly tipsy in the kitchen to dangerously passionate in the bedroom.

The second time she slept with Mark Sloan was Derek's second straight week of forty-hour shifts, and that time she was sober. Shockingly sober. Unbecomingly, indiscreetly, ashamedly sober. The truth was, Mark Sloan offered a very tempting type of therapy. Mark Sloan was even more scary and damaged than Addison, and the idea that she would survive if Mark survived was soothing, especially as he seemed to be thriving in her presence. Mark was pleasure free from pain. He was sneaking out of your parents' house at fifteen and making out in parked cars. Mark was fun, Mark was free.

And, in her defense, Mark started it. He was the one who touched her with his dirty manwhore hands and he was the one who kissed her with his grimy, Casanova lips and he was the one who'd reached up and wiped a stupid tear off of her cheek.

Mark was the one who chased her when she left for Seattle. Mark was the one who'd lied about the bet to save her integrity.

She likes to say Mark started it, but she knows that isn't true.