Exaggerate or overdo, especially with extravagant emotion, as in Hamming up the eulogy was disgraceful, especially since he didn't even know the deceased. It is also put as , meaning "overact," as in She loves to ham it up in front of the class. This idiom probably alludes to the hamfat (lard) used to remove stage makeup, mentioned in the minstrel song, "The Ham-Fat Man." From this hamfatter came to mean "an inexpert and flamboyant actor," and was in the late 1800s shortened to ham. The idiom here was first recorded in 1933.
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