Johnny Galecki stars in The Big Bang Theory as Leonard Hofstadter, a physicist at Caltech. Leonard is the more social of his nerd friends.
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Jim Parsons stars on The Big Bang Theory as Sheldon, Leonard's best friend, co-worker and roommate. Sheldon is definitely the smarter and nerdier of the two.
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Penny meets Leonard's cute new co-worker, Dave (guest star Michael Trucco) and has an immediate crush on the cute new physicist / bad boy.
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A picture of Sheldon and Leonard from the series premiere of The Big Bang Theory. Sheldon and Leonard are geeks but Leonard wants more than this socially awkward roommate.
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Sheldon and Leonard go over the roommate bylaws now that Sheldon considers Leonard's new girlfriend a roommate and they have new rules to go over.
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Sheldon comes to Penny for help when he wants to make sure Leonard secures Stephanie as his girlfriend. He uses some casual talk that's pretty damn funny in order to get Penny to help him.
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The poster from the CBS sitcom The Big Bang Theory starring Johnny Galecki, Jim Parsons, and Kaley Cuoco.
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TBBT Quotes

Penny: Here's a question-- as an alien pretending to be human, are you planning to engage in any post-prom mating rituals with Amy?
Sheldon: There are post-prom mating rituals?
Penny: Not always. Unless your date drives a van with an air mattress, then always.
Sheldon: Well, if it's part of the prom experience, then I'm open to it.
Penny: You're kidding.
Sheldon: I may be an alien, but I have urges.If Amy wants to copulate by firing her eggs into space, well, then, I will happily catch them with the reproductive sac on my upper flermin. I'm not the best at reading facial cues, but I can see that you're a little turned on.

Penny, there's only one cookie with something in the middle that solves life's problems, and that's an Oreo. Or a Nutter Butter, if you're in a pinch.

Sheldon