When something is so ugly that when you see it, it actively makes you mutter "Fuck." due to the enormous amount of stress caused by knowing it's horrid existence and the fact that people will meet this thing. "Fuck" is also muttered for the creator as an obligation since the creator clearly should've realized he/she has fucked up while making it and stopped making it.
Oliver: Hey Jacob have you seen Sonic in the new movie?
Jacob: No. Why?
Oliver: I'm telling you Sonic is Fuck Ugly dude.
someone that is so ugly that you would fuck them. in fact this person is so ugly one can take pride in having done the naughty deed with them under the conditions of the amount of effort it would have taken to find such a hideous person.
Oh man, that girl is so fuck ugly, I mean she has to be the grossest girl I have ever seen! I totally need her in bed.