I shit you not en · X
Etymology
Earliest known use is from 1949 in Dan Levin's Mask of Glory.
Meanings
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(vulgar) Synonym of I kid you not (Used to insist that one is telling the truth)
“What’sa matter?” Mudgen asked. “Ain’t you ever seen snow before?” But he couldn't keep himself from going over to the door. “Well I shit you not it is snowing!”
1954, Robert James Collas Lowry, “Casualty”, in Happy New Year, Kamerades!, Doubleday & Company, page 106: