Sheldon, Howard, and Leonard give a presentation about careers in science to a group of girls in junior high on The Big Bang Theory. "The Contractual Obligation Implementation" is the 18th episode of the shows sixth season.
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Koothrapali refuses to leave his apartment after a bad date on The Big Bang Theory. "The Monster Isolation" is the 17th episode of the show's sixth season.
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Who would guess that Penny and Leonard's Valentine's day wouldn't go as planned on The Big Bang Theory? "The Tangilble Affection of Proof" is the 16th episode of the show's sixth season.
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Leonard and Sheldon's fight spills over into everyone else's lives on The Big Bang Theory. "The Spoiler Alert Segmentation" is the 15th episode of the show's sixth season.
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Game night turns into a messy battle of the sexes on The Big Bang Theory. "Re-Entry Minimization" is the fourth episode of the show's sixth season.
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Sheldon tries to intervene when he discovers a secret about Penny and Leonard on The Big Bang Theory. "The Decoupling Fluctuation" is the second episode of the show's sixth season.
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Raj chills with Leonard and Penny on the sixth season premiere of The Big Bang Theory, titled "The Date Night Variable."
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The Big Bang Theory boys are back! This is a photo from the Season 6 premiere.
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Leonard and Sheldon are all dressed up for Howard and Bernadette's wedding on The Big Bang Theory. "The Countdown Reflection" is the 24th episode and season finale of the show's 5th season.
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Whoa, what's going on here?!? The gang looks down at Sheldon's odd hairstyle in this scene from The Big Bang Theory.
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Sheldon is a nice guy. But he can also be a very demanding friend toward Leonard, as evidenced here.
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They're back together! All seems right in the world when Penny is dating Leonard, don't you agree?
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TBBT Quotes

Penny: Hey, Sheldon, did you change your Wi-Fi password again?
Sheldon: Yes, it's "Penny, get your own Wi-Fi." No spaces.

Bernadette: I had a plan. I kept leaving Dove bar wrappers around to explain any weight gain.
Amy: Where did you get empty Dove bar wrappers?
Bernadette: From all the DOVE BARS I ATE. I'M PREGNANT. Try to keep up!