What does the phrase butt ugly mean?

Butt ugly is an informal expression used to describe something or someone considered extremely ugly or unattractive. It's an emphatic way of conveying a strong sense of disdain for the appearance of something or someone. The term "butt" doesn't have any literal significance here and is only used for emphasis. Butt ugly is considered somewhat crude and informal in tone, though its usage might vary in different contexts and cultures.