Episode 11, "Favors"
Here we thought Sally's age of innocence was tossed out the window when she caught Roger receiving an oral examination from Marie Calvet. Boy, were we wrong. Nothing can compare to the sheer revulsion of walking in on your father getting it on with not only a woman who is not his wife, but the mother of your current crush. Sally had snuck into the Rosens' apartment to retrieve an "I like you" letter for Arnold and Sylvia's 19-year-old son, Mitchell, but she left with a damaged soul – and Don, having unwisely rekindled his affair with his downstairs neighbor, lost the love and support of the one female he still trusted and respected. Most likely forever. No longer can he weasel his way out of such compromising situations by calling what he did "comforting Mrs. Rosen," because Sally isn't a naïve little girl anymore. She sure as hell didn't need to grow up in a brothel to get the same tawdry life lessons as her father.