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Someone kind of dull, dim, unimpressive, slightly south of mediocre
You know, Joe is kind of a thirty watt bulb, barely got into community college, flunked out after 1 semester as a part time student, now barely keeps his job at the 7 Eleven.

Girl: Uh..... I'm way out of your league. Me: Yale grad, doctor. You: thirty watt bulb.
by zadok the beast April 10, 2009
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