Butter wouldn't melt in his mouth proverb
The phrase can be used after "look as if".
Used to imply that someone is acting as if he or she is demure, innocent, sincere or reserved but they may be not
Stacy looked so calm as though butter wouldn't melt in her mouth, but I knew better.
Peter looks as if butter wouldn't melt in his mouth when he's around girls, but in fact he is a playboy.
Lucy looks as if butter wouldn't melt in her mouth. Sooner or later you will see what she is really like.
Don’t be fooled by Jennie's good behaviour. She looked as if butter wouldn't melt in her mouth.
White lie
Seem to be very suspicious or morally unacceptable
To be dishonest or deceptive and no one can believe
Very dishonest and deceptive
We can change the possessive adjective from his into my, her, your, their, our or one's.
This phrase is old, usually used in a critical sense and was most often used to describe women (in the past at least). It was listed as a proverb in 1562 in the work The Proverbs and Epigrams of John Heywood and in Lesclarcissement de la langue françoyse in 1530.
Used to allude that the last force, problem or burden which is seemingly minor and small causes a person, system or organisation to collapse or fail
Her husband's violent act last night was the straw that broke the donkey's back and she left him