butter wouldn't melt

butter wouldn't melt (in (one's) mouth)

Said of one who appears innocent or reserved in certain company, when in fact one may have the opposite demeanor. Sure, he looks as if butter wouldn't melt in his mouth when he's around people he doesn't know, but stay a while and you'll see what he's really like.
See also: butter, melt

butter wouldn't melt (in someone's mouth)

Prov. Someone is acting as if innocent. By the time her parents came home, Emily had cleaned up all evidence of having broken the valuable figurine, and she looked as though butter wouldn't melt in her mouth. Jane: How can you suspect George of playing that practical joke on you? He looks so innocent. Jill: Yes, butter wouldn't melt, I'm sure.
See also: butter, melt

ˌbutter wouldn’t ˈmelt (in somebody’s ˈmouth)

(spoken) a person looks very innocent, but probably is not: She looks as if butter wouldn’t melt in her mouth, but don’t be fooled by first impressions!
See also: butter, melt
References in classic literature ?
There's old Stephen Grant coming in," exclaimed Peg viciously, shaking her floury fist at him, "and looking as if butter wouldn't melt in his mouth.
Jock' Horner they call him, so quiet-like an' easy-goin', soft-spoken as a girl, till ye'd think butter wouldn't melt in the mouth iv him.
These mean, soft chaps, that you would think butter wouldn't melt in their mouths, were the ones to make a wom- an thoroughly miserable.
NAME: Bertie APPEARANCE: Butter wouldn't melt SPECIAL SKILLS: It's apt that this puss appears the week after Ron Moody - Fagin in Oliver
When you first meet him you'd think butter wouldn't melt, but after a while he comes out of his shell.
LITTLE Prince George looks like butter wouldn't melt in his mouth as he smiles for the camera wearing a smart white shirt and ceremonial guard knit, his hair in a neat side parting.
Taylor Swift The singer looks like butter wouldn't melt in this angelic frock, as she pairs a lace dress with her signature red lippy and nude accessories.
All right, so she's fallen out with KATHERINE JENKINS and ALED JONES, but she sang like butter wouldn't melt at the Jazz Pizza Express in London's Soho on Wednesday.
She may be adorable and look like butter wouldn't melt in her mouth but greyhound Jasmine sparked a full-blown gas scare at a housing estate.
Andrew Castle - like the politically correct, butter wouldn't melt in his mouth wimp that he is - said: "I know he's upset but I must apologise for the language.
FRIDAY Don't let the butter wouldn't melt look fool you, Simon Amstell combines vulnerability with razor sharp wit and a talent for provocation.
Another parent added: "She was so prim and proper, the sort where butter wouldn't melt, she came to visit me at home when I first enrolled my child for school.
I've said it before Vicar," she began, looking for all the world like butter wouldn't melt in her mouth.
TO look at Sarah Millican you would think butter wouldn't melt in her mouth.
Pointing out a picture of Dan when he was younger, Fiona said: "He looks like butter wouldn't melt but he was a little devil really, a right character.