The grotesque remnants of a human fingernail lingering on a finger that was partially severed by a lawnmower. The nail accurately resembles the horn of an African rhinoceros and gives nightmares to everyone that encounters it.
Guy 1: What the fuck is up with that guy's fingernail?
Guy 2: Yeah, supposedly he stuck it into a lawn mower a few years ago, while it was running!
Guy 1: It looks like the horn of a rhinoceros!
Guy 2: It's a total fingerhorn.