Sheldon: You know, using positive reinforcement techniques, I could train that behavior out of her in a week.
Leonard: No.
Sheldon: If you let me use negative reinforcement, I can get it done before we go to bed.
Leonard: You're not squirting her in the face with water.
Sheldon: No, of course not. Were talking very mild electric shocks. No tissue damage whatsoever.

Sheldon: Oh, come on, you can't tell me that you're not intrigued about the possibility of building a better girlfriend.
Leonard: I'm not. And Penny's qualities, both good and bad, are what make her who she is.
Sheldon: You mean, like that high-pitched, irritating laugh?
Leonard: Yes.
Sheldon You wouldn't prefer a throaty chuckle?
Leonard: You're not changing how Penny laughs.
Sheldon: No, that would be incongruous, I was going to lower the whole voice to a more pleasing register.

Raj: Are you seriously going to deface your body just for the possibility you could have cheap sex with a strange girl you met in a bar?
Howard: Uh, yeah!
Raj: What is your mother going to say?
Howard: She's not going to see it. She takes my temperature orally now.

Sheldon: Well, I'm going to make some warm milk and then turn in. I trust if you two are planning in engaging in amorous activities, you'll keep the decibel level to a minimum.

Sheldon: There are more things in Heaven and Earth, Horatio, than are dreamt of in your philosophy.