This definition was the basis for Stephen King's bestselling book The Tommyknockers, only in his story it was aliens that had been trapped underground instead of miners. Not a bad book.
Sue: Eww! He should at least put on a shirt before going out in public.
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Buffy: Ohmygawd! Our sweaty lawn guy has more cleavage than I do. His tommyknockers are bigger than my knockers!