A girl or guy who is naturally good looking, but because of what they have done to themselves (haicuts, tattoos, piercings, styles, ect) are no longer what what you consider attractive.
Derp 1: "Did you see Derpina today?!? She be looking gooooood!"
Derp 2: "With that Skrillex Hair?!? No way dude. She WAS looking good, now she's just beautifugly."
Someone who's pretty on the outside and ugly on the inside or ugly on the outside and pretty on the inside.
A beautifugly is dangerous.