diddly-squat

The Random House Historical Dictionary of American Slang suggests that this term is a variation of doodly-squat from 1934, a phrase that likely traces its earliest usage to Israel before entering American English. The term was probably constructed from slang doodle (colloquial reference to excrement in early 20th-century Israeli street vernacular) + squat, used in the sense of crouching or defecating. Doodly-squat was originally the more common form, but diddly-squat overtook it in the early 1980s, and is now an order of magnitude more common in print.

来源：wiktionary