Chinese Idiom: Nice on the Outside, Rotten on the inside

Hilarious! This is a Chinese idiom, but this translation given to Froog is much more colourful.

“The seemingly bright and colourful overcoat could not possibly cover up the patched underwear beneath.”

金玉其外, 败絮其中

jīn​yù​qí​wài​, bài​xù​qí​zhōng, or “gilded exterior, shabby and ruined on the inside (idiom)”, or my dictionary says “rubbish coated in gold and jade”.