At the beginning of "Name of the Game" (Season 2) Meredith swears off men and booze. While at the bar. Derek and Addison react awkwardly.
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Grey's Anatomy Season 2 Episode 22 Quotes

ADDISON: "Dr. O'Malley, did you get Molly Thompson's test results back from the lab yet?"
GEORGE: [pauses] "No."
ADDISON: "What? Dr. O'Malley, when I assign you to a case, I expect you to give it your undivided attention. Give me one good reason I shouldn't take you off this case!"
GEORGE: [pauses] "I just discovered that Molly Thompson's maiden name is Grey, making her the daughter of Thatcher Grey, meaning that Meredith has a sister she doesn't even know exists. And I don’t care. I don’t. I'm on this case. and... apparently God hates me."
ADDISON: "Okay."
GEORGE: "Thanks."

[narrating] "So go ahead. Argue with the ref, change the rules. Cheat a little, take a break and tend to your wounds. But play. Play. Play hard, play fast... play loose and free. Play as if there were no tomorrow. It's not whether you win or lose, it's how you play the game... right?

MEREDITH