Originates from Smodcast (Kevin Smith and Scott Mosier podcast) Episode 91 at the 52:44 mark where guest Malcolm Ingram credits uber-producer Scott Mosier with the genesis of the term.
Man 1: I’m supposed to visit my late wife tomorrow, but I’m afraid it’s going to rain.
Man 2: What!?! That’s good news! Bring some towels… you’re about to get your first mud nutt!!
I’m going to my late lovers grave because I gotta get that mud nutt.