When two individuals engage in oral sex immediately after having sexual intercourse. Derived from the animal itself, ducks eat the stuff off the grass after a rainfall, like oral sex after sex.
When a female takes two Pringles and inserts them inside her vagina. One of the Pringles is upside down creating a duck bill. After this the male fucks her through the hole. Thus a Duck Fuck.
Dyson: " oh I finally got my dickinside Mikayla's bill. It was a mean Duck Fuck!"