When you fuck a poopy asshole and decide to keep your dick poop-covered and put it in your pants for the day.
See Rutty duck for a different spelling.
Dude, my ruddy duck is still nice and juicy from Sharmayne's asshole.
A type of duck iOxyura jamaicensis/i, native to the Americas, and an introduced bird in parts of Europe (in some places in Europe it is regarded as a nuisance).
Wikipedia has a good article on the ruddy duck.