When you've sat on the toilet for so long the bathroom light sensor has timed out, leaving you to finish dropping a Duece in the dark. This mostly takes place at the office or public establishments. Noc is short for nocturnal. By the time you're ready to wipe you can see like a jaguar in a pitch black bathroom stall.
"I haven seen John in about 30 minutes".
"I bet he's Noc Duecing. He's got some serious IBS"