The Big Bang Theory Season 1 Episode 14

Sheldon: Why'd you set it for the day before yesterday?
Leonard: Because I want to go back and keep myself from getting a time machine.
Sheldon: You can't. If you were to prevent yourself from buying it in the past, you would not have it available in the present – travel back and stop yourself from buying it, ergo you would still have it. This is a classic rookie time travel mistake.
Leonard: Can I go back and prevent you from explaining that to me?
Sheldon: Same paradox—if you were to travel back in time and, say, knock me unconscious, you would not then have the conversation that irritated you, motivating you to go back and knock me unconscious.
Leonard: What if I knocked you unconscious right now?

Leonard: Come on, guys, push!
Howard: If I push any harder I'm gonna give birth to my colon.
Raj: I can't feel my fingers. Hurry up!
Sheldon: It's the same amount of work no matter how fast you go—basic physics.
Raj: Sheldon, if my fingers ever work again, I've got a job for the middle one.

Leonard: The elevator's been broken for two years.
Sheldon: I've been meaning to ask you. Do you think we should make a call about that?
Howard: Not necessary. I have a Masters in Engineering. I remotely repair satellites in a regular basis. I troubleshoot space shuttle payloads. When the Mars Rover started pulling to the left I performed a front-end alignment from 62 million miles away. (pushes the button of the broken elevator and then listens if it comes down) No, that baby's broken.

Leonard: Girls like Penny never end up with guys who own time machines.
Sheldon: I disagree. Your inability to successfully woo Penny long predates your acquisition of the time machine. That failure clearly stands on its own.
Leonard: Thanks for pointing it out.
Sheldon: In addition, your premise is flawed. In the original film, Rod Taylor got Yvette Mimieux with that very time machine. In Back to the Future, Marty McFly got the opportunity to hook up with his extremely attractive young mother.
Leonard: Those are movies.
Sheldon: Of course they're movies. Were you expecting me to come up with an example involving a real-life time machine? That's absurd.

Sheldon: You hypocrite!
Penny: What?
Sheldon: Little Miss 'Grown-ups don't play with toys', if I went into that apartment right now, would I not find Beanie Babies? Are you not an accumulator of Care Bears and My Little Ponies? And who is that Japanese feline I see frolicking on your shorts? Hello, Hello Kitty!

Sheldon: Are you upset about something?
Leonard: What was your first clue?
Sheldon: Well, it was a number of things: first, the late hour; then your demeanor seems very low energy; plus your irritability...
Leonard: Yes, I'm upset!
Sheldon: Huh, I don't usually pick up on those things. Good for me.
Leonard: Yeah, good for you.
Sheldon: Oh, wait, did you want to talk about it?
Leonard: I don't know, maybe.
Sheldon: Wow, I'm on fire tonight.

Sheldon: I propose we add 'pants must be worn at all times in the time machine'.
Leonard: Seconded.
Howard: I was gonna put down a towel.

Leonard: Hey, if you wait for us to set up the time machine, I can drop you off at work yesterday—time travel joke. It's not—never mind.
Sheldon: For what it's worth, I thought it was humorous. (fake laughs)

Penny: (to Leonard) Look, you are a great guy, and it is the things you love that make you who you are.
Howard: I guess that makes me large breasts.