Ugly as sin / face only a mother could love
Acordou com cara de cão chupando manga depois daquela festa.
He woke up looking ugly as sin after that party.
Cão here is a Northeastern euphemism for the devil — calling him 'the dog' to avoid naming him directly. The image of the devil sucking on a fibrous mango — squinting, grimacing — gives the picture of the ugliest possible expression.
Falando's Idiom Trainer teaches you to recognize idiom meanings and create sentences using them, so you can speak like a Brazilian.