Cosby was starring in The Bill Cosby Show, which ran from 1969-71, and in which he played a physical education teacher at a Los Angeles high school.
Tarshis now claims what she thought was a mentorship soon turned into a nightmare. This week, with a scandal exploding over several women's past and current accusations that Cosby sexually assaulted them, she told her story for the first time, she says, to "support the women who came before me."
Cosby has denied the accusations, though his publicist and lawyers have not responded to requests to address Tarshis's claims specifically. One of his attorneys, John Schmitt, issued a statement Sunday, before Tarshis first spoke out, saying that just because the allegations are being repeated "does not make them true." He said his client would make no further comments.
"I met him through friends who knew him, and they lunched with him at his bungalow on the set in between shooting the show," she says.
"They invited me to go along," she says. "Then I was asked to come back to a few other lunches and I did."
He made her Bloody Marys, which he topped with a little bit of beer and called "Red Eyes," she says.
"He was very charming. Kinda funny. Kinda quiet," says Tarshis, a former publicist and journalist. "He was very free with the food and drinks. I noticed he wasn't drinking anything, though."
After learning she was an aspiring comedy writer, Cosby invited her to his bungalow alone, she alleges.
"He said, 'Come up to my bungalow after I'm done shooting and we'll work on the bit together,' " she says. "I thought, 'That's really cool. Getting to work with Bill Cosby will be a great credit.' "
When she got here, he made her his usual "Red Eye," she says.
According to Tarshis, the next thing she knew, she woke up.
"I was lying on the couch and he was removing my underwear," she says. "I said, 'What's going on?' He said 'You know what's going on.' "
She claims she quickly told him she had a sexual disease (she didn't) and he'd catch it, which would alert his wife he was cheating on her.
"He thought quicker and had me perform oral sex on him," she says, "which was even more horrible."
After he was finished, he "acted like nothing happened," she says.
"I got up feeling sickened, embarrassed, humiliated," she says, "and he's sort of saying, 'Well, we really need to work on this monologue some more.' "
She got dressed and he gave her $10 or $20 and said, "Let me call a cab for you," she says.
"I'm thinking, 'You did this to me and now you can't even get me home? You're just sending me out with a cab,' " she says.
But she took the money and left – and told no one.
"I was scared," she says.
Another EncounterTarshis went home to her parents in Brooklyn, where Cosby called her about a month later, she says.
"My mother answers the phone and he said, 'I'm going to pick up your talented daughter and I want to take her to the Westbury Music Fair so she can see the monologue she wrote for me.' "
Her mom handed her the phone.
"I had no way out," she says. "He was being really charming and I didn't want to tell my parents, 'This guy [sexually assaulted] me. I don't want to go out with him.' For some reason, I just couldn't tell them."
So she agreed to go with him. According to Tarshis, his driver picked her up at her parents' home and took her to Cosby's hotel in Manhattan, where she went up to his suite.
"He offered me a Red Eye," she says. "He was being really friendly and I was uncomfortable. But I had the drink and we left."
"I had another glass of wine or soda in the car," she says. "I began to feel a little bit funny."
Cosby had no seat reserved for her, so she and the chauffeur stood in the back of the theater.
"I started to get really, really drugged, so much that I told the chauffeur, 'I have to go back and sit in the car. I can't stand up,' " she says.
She recalls she went to the limo and collapsed inside.
"The next thing I remember is waking up naked in the bed with Cosby the next morning with him naked next to me," she says. "I have no idea what happened."
Once again he "acted like nothing happened," she says.
"He said, 'We'll write together sometime,' " she says. "I think I just got myself in a cab and let my parents give me the money for the cab when I got home."
Cosby called her a couple more times at her parents' home, she says.
"He'd say, 'How are you doing?' she says. "And I'd say, 'I'm doing very well. Thank you.' And hang up the phone.
She says she never saw or spoke to him again.
And she never told a soul about either incident until she confided in a friend 20 years later.
Sharing Her StoryWhoopi Goldberg has come out and said, 'Why didn't you go the hospital?' " she says. "They didn't have rape kits back then. And I didn't think about it. I was disgusted. I just wanted to get away from him."
Tarshis says decided to go public with her story now because of the recent resurfacing of sexual assault allegations against Cosby.
"I just really thought it was time for me to come forward and support the women who have come before me – for the people who don't believe them," she says.
"For the people who believe his image, that he's Dr. Huxtable, America's greatest father," she says.
"And if there's other women he's still contemplating doing this with maybe they'll read this and not think, 'Oh. This will never happen to me.' "