Most people say DIDDLY SQUAT: https://books.google.com/ngrams/graph?content=diddly+squat%2C+doodley+squat&year_start=1800&year_end=2000&corpus=15&smoothing=3&share=&direct_url=t1%3B%2Cdiddly%20squat%3B%2Cc0%3B.t1%3B%2Cdoodley%20squat%3B%2Cc0