When Sheldon crashes in on Stuart (Kevin Sussman) and Penny's date, he ends up arguing with Stuart on comic books until they put Penny and Stuart's chances of getting lucky to sleep.
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Leonard, Raj and Wolowitz head out to a local bar for Ladies' night. Wolowitz explains to Raj why he can't order a girlie drink during Ladies' night.
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Stuart (Kevin Sussman) flirts with Penny as he givers her a portrait he drew of her in exchange for her phone number. Wow, Penny is falling for the nerds hardcore now.
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Stuart (Kevin Sussman) comes over to offer help to Leonard and Penny as they attempt to pick up a comic book for Penny's nephew. Stuart is nice... for a guy who likes comic books.
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The Big Bang Theory Season 2 Episode 20 Quotes

Raj: The Wolowitz coefficient?
Wolowitz: Neediness times dress size squared

Leonard: But we all agreed the third Thursday of every month will be "Anything Can Happen Thursday"
Sheldon: Apparently the news didn't reach my digestive system, which when startled has it's own version of "Anything Can Happen Thursday"