butter wouldn't melt in someone's mouth

1.
UKUSgeneral Englishinformalcolloquial
- To appear, outwardly, extremely demure, prim, or innocent; to give the impression of being incapable of impoliteness or impropriety.
2.
UKUSgeneral Englishinformalcolloquialironic
- Used ironically to suggest that a person who appears meek or harmless is in fact disingenuous, calculating, or capable of sharp behavior.

Examples:

No examples available.