When a German songwriter hires Jamaicans (and Arubans) to sing/lip-sync/front a 70s disco band because his cracker style wasn't making it, i.e., Boney M.
Similar to Godwin's Law, Germain's Law states that, in an argument/debate/slanging match, the first person to reference the other person's mother automatically loses.
Guy 1: You totally stole that from a bumper sticker.
Guy 2: It wasn't from a bumper sticker, it was your mum's ass tattoo.