I love it when Sheldon doesn't get a joke, or overexplains it and that sort of thing, but it kind of makes me feel sorry for him because he doesn't get why he doesn't get it or why explaining it isn't funny. Brings out the "aww, my baby Shelly" instinct, somehow.
The best expample to me is that one episode when Bernie announces that her dissertation was accepted.
When they're all making fun of Leonard's gaseousness and Sheldon says something that makes everyone laugh, but he doesn't really get it at first and looks around the table, and only laughs because everyone else is. And then it happens again. It's not until about the third time that he kind of realizes why things are funny, but then he kind of unintentionally ruins the funny moment.
Poor Shelly.
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"I'm vilifying you--for God's sake, pay attention!"
"Wherever the music takes me, kitten!"
Jim Parsons read my poem on UK radio!