noun: A large, flashy peice of neck jewelry (ie: chain, medallion etc)worn by a male-usually a badass-during sexual intercourse, for the sole purpose of watching the "fuck-chain" swing during sex. "fuck-chains" are most often worn during doggy stlye sex so the fuck-chainer can watch it tap against the ass of the fuck-chainee.
"that's a nice fuck-chain man, whered u get it?"
"you ready to get boned? hold on lemme put my fuck-chain on real quick."