Fuckin's are the viscous by product of fucking that typically run down the crack of the female’s ass or snooch (depending of course on whether she is facing up or down). Fuckin’s are sometimes consumed by absent minded males who perform cunnilingus on a female in which he has already busted a ferocious nut. This act is known as "eatin' your own fuckin's" and is thought to be de rigeur among perverts of Western Europe and the Southeastern United States.
"Mary and I had a foursome the other night with Jim and Bettysue". "I saw ol' Jim eat his own fuckin's and then after we switched partners he ate mine too".