When someone your working with doesn't know anything
Well I thought John knew the area well, but he doesn't know diddley fuck.
To do absolutely nothing of importance for a period of time.
"What have you been up to?"
"Who me? I've been up to sweet diddley fuck"
To do nothing. The word fuck at the end makes it worse than just doing jack diddley.
All my coworkers do all day is jack diddley fuck and I always have to clean up after the lazy bastards.