• From “Pilot” (Season 1):
Leonard defends his enthusiasm for Penny’s job at the Cheesecake Factory.
Leonard: I love cheesecake.
Sheldon: You’re lactose intolerant.
Leonard: I don’t eat it. I just think it’s a good idea.
• From “The Big Bran Hypothesis” (Season 1):
Leonard is frustrated with Sheldon’s inability to understand sarcasm.
Leonard: For God’s sake, Sheldon, do I have to hold up a sarcasm sign every time I open my mouth?
Sheldon: You have a sarcasm sign?
• From “The Cooper-Hofstadter Polarization” (Season 1):
Leonard: You are not Isaac Newton.
Sheldon: No, no, that’s true. Gravity would have been apparent to me without the apple.
• From “The Pancake Batter Anomaly” (Season 1):
Sheldon is recalling a time when he was sick.
Sheldon: Anyway, the housekeeper in the faculty residence didn’t speak any English. When I finally managed to convince her I was sick, she said, “Möchtest du eine Darmspülung?”
Penny: What does that mean?
Sheldon: Based on what happened next, I assume it means, “Would you like an enema?”
• From “The Hofstadter Isotope” (Season 2):
Howard: I am a horny engineer; I never joke about math or sex.
• From “The Bad Fish Paradigm” (Season 2):
Sheldon is staying over at Howard and Raj’s place.
Howard: How’s the air mattress?
Sheldon: It’s okay, if you don’t mind sleeping on a bouncy castle.
• From “The Griffin Equivalency” (Season 2):
Sheldon: I often forget other people have limitations. It’s so sad.
Howard: He can feel sadness?
Leonard: Not really. It’s what you and I would call condescension.
• From “The Killer Robot Instability” (Season 2):
The guys have created a robot for a competition.
Sheldon: Is it wrong to say I love our killer robot?
Raj: As with my father I both love and fear it.
• From “The Work Song Nanocluster” (Season 2):
Howard is sick of Raj’s complaints about his upbringing.
Howard: Oh, stop it with the fake third-world crap. Your father is a gynecologist, and you had a house full of servants.
Raj: We only had four servants, and two of them were children.
• From “The Electric Can Opener Fluctuation” (Season 3):
Penny tries to sympathize with Sheldon after he learns his scientific results were invalid.
Penny: Sheldon, you know, I do understand what you’re going through.
Sheldon: Really? Did you just have the Nobel Prize in waitressing stolen from you?
• From “The Jiminy Conjecture” (Season 3):
Raj is uneasy about accompanying Sheldon and Howard to catch a cricket.
Raj: I don’t like bugs, okay? They freak me out.
Sheldon: Interesting. You’re afraid of insects and women. Ladybugs must render you catatonic.
• From “The Gorilla Experiment” (Season 3):
Penny is upset because she feels she isn’t smart enough for Leonard.
Sheldon: Why are you crying?
Penny: Because I’m stupid!
Sheldon: That’s no reason to cry. One cries because one is sad. For example, I cry because others are stupid, and that makes me sad.