Fuck-in-Law Share definition Flag The relationship you have with anyone that has already had sex with the person you’re currently sleeping with. Bob banged Susan at that party last year, guess that makes us fuck-in-laws. Fuck-in-Law by Sigar Cel November 25, 2003 0 0 Get merch Get the Fuck-in-Law mug. Buy Now — $32.95 See more merch