dum-dum
n.— «When he returned in ’03, McLain was equipped with a thick cushion to wear atop his helmet (he refers to it as a “dum-dum”), which softened any potentially dangerous blows to the head.» —“McLain Making Progress” by Mitch Dobbs ‘Bama (Al.) June 24, 2004. (source: Double-Tongued Dictionary)
Further reading
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Some TV commercials launch catchphrases that stick around long after the original ads. The exclamation Good stuff, Maynard! is still a compliment almost 40 years after it was used in a commercial for Malt-O-Meal hot cereal. And: what do you call...