Sheldon: Jacuzzi is a commercial brand, hot tub is the generic term, i.e., all Jacuzzis are hot tubs, but not all hot tubs are Jacuzzis.
Zack: Is that like all thumbs are fingers but not all fingers are thumbs?
Sheldon: Surprisingly, yes.
Zack: Nice! Now what exactly are toes?

Zack: One question. How can you be sure it won't blow up?
Leonard: The laser?
Zack: The moon.

Leonard: Don't worry about the moon. We, we set our laser to stun.
Zack: Smart.
Leonard: Now, we'll be able to see the beam when it leaves, but it won't be strong enough when it comes back to be seen by the naked eye.
Zack: (chuckling) Naked.

Zack: Is that the laser? It's bitchin'.
Sheldon: Yes. In 1917, when Albert Einstein established the theoretic foundation for the laser in his paper "Zur Quantentheorie der Strahlung", his fondest hope was that the resultant device be bitchin'.
Zack: Well, mission accomplished!

Wolowitz: Raj, did you ever tell your sister about the time Sheldon got punched by Bill Gates?
Priya: Oh, God, you're kidding.
Raj: No, Gates gave a speech at the university. Sheldon went up to him afterwards and said, "Maybe if you weren't so distracted by sick children in Africa you could have put a little more thought into Windows Vista."
Leonard: Bam, right in the nose. Made me proud to own a PC.

Sheldon:He'll be back.
Leonard: (Through the door) Of course, I'll be back, I live here!

Amy: Y'know, if being on your own is new to you, I'd be happy to share some tension-relieving techniques for ladies I've perfected over the years. For example, do you own an electric toothbrush?
Penny: No
Amy: You should get one!