That would be The Isolation Permutation. Amy is hurt because she learns that Penny & Bernadette went dress shopping without her. After trying to reach Amy with every electronic device he has, Sheldon becomes worried when she doesn't respond. He & Leonard go to Amy's apartment to check on her, where Sheldon hears her playing her harp & singing REM's 'Everybody Hurts', then decides it's a bad idea to go & see her, for she'll be too emotional, but before he's able to leave, Leonard tells him he needs to step up & be a man, knocks on Amy's door 3 times (calling out 'Amy, Amy, Amy' in between each knock), then leaves Sheldon standing at the door. After asking Sheldon why he came over & he responds by telling her she didn't respond to any of his electronic communication devices Amy informs him that she didn't respond because she wanted to be left alone. Depressed & feeling rejected by Penny & Bernadette, Amy turns to Sheldon and asks him to 'keep an open mind'...He responds with one simple word: 'Always'. Amy then asks Sheldon to make love to her. He comes up with a counter proposal, saying he will stroke her head & repeat, "Aw, who's a good Amy?". Amy then has a counter proposal of her own: "French kissing, 7 minutes in Heaven, culminating in 2nd base.". Sheldon offers a 2nd counter proposal: Neck massage & getting him a beverage. Amy decides to make one more counter proposal, which is that they cuddle. Sheldon agrees to her request
What does Sheldon say in response to Leonard's commenting about Albert Einstein's sex life?