Sheldon is an extreme Aspie; Leonard is Aspie as well, I think, but has made adjustments to the world. (Incidentally, Sheldon Leonard is also the name of a legendary TV producer, responsible for shows like "The Andy Griffith Show", its spinoff "Gomer Pyle, USMC", "The Dick Van Dyke Show", "I Spy", and "My World and Welcome To It".)
Rajnesh might be Aspie as well, and has had my single favorite line of the series so far (on his father wanting Raj to be a famous gynecologist, like him: "I can barely manage to look a woman in the eye!"); Howard seems more like a supremely misinformed nerd.
Penny's just cute. 
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Sodium is a metal that reacts explosively when exposed to water. Chlorine is a gas that'll kill you dead in moments. Together they make my fries taste good.