Bum Dip
The act of ejaculating on your finger and sticking said finger in ones anus thus allowing the fecal matter to stick. The finger is then licked or sucked. Similar to the popular candy, "Fun Dip" Where you lick a sugary rod and stick it into a packet of sugar allowing the sugar to stick.
Samantha and I were feeling frisky and decided to eat each other's bum dip.