“ugly as fuck”
is usually meant as an insult, though it shouldn’t insult, rather compliment. fuck in its original definition is the act of sex, sex is a beautiful thing always has been, always will. now this only way this insult could actually be legitimate was if a bad part of sex was focused on, “ugly as necrophilia” or “ugly as rape”, other than that, its just used by stupid, intellectually stunted people who cant think of a better word than fuck to describe how ugly something is, try using your brain once in a while.