A racially and culturally insensitive word derived from 15th and 16th English views of Irish and Scottish peasants with Celtic accents and customs. English nobility nicknamed these people "Crackers" because whenever they spoke, it makes the English laugh at them. Hence, the phrase, "to crack a joke" or a "cracker" was intended for Irish and Scottish peasants who sounded funny when spoke, were being interrogated or tortured.
English Lord #1: I'm bored and need a good laugh, but I'm sick of calling the jester.
English Lord #2: I know, let's arrest some Crackers and interrogate them while we drink some ale!
English Lord #1: Brilliant! They are exceptionally entertaining under lashing!
English Lord #2: Especially when forcing them to beg for mercy!
English Lord #1: Last time, even the inquisitor could not stop laughing!
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