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

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

butter wouldn't melt in one's mouth

Be overly coy or demure; be insincere. For example, She looked quite innocent, as though butter wouldn't melt in her mouth, but we knew better . Already a proverb in John Heywood's collection of 1546, this metaphoric expression alleges that one is literally so cool that butter inside the mouth would not melt.
See also: butter, melt, mouth

butter wouldn't melt in someone's mouth

If you say that butter wouldn't melt in someone's mouth, you mean that although they look completely innocent, they are capable of doing bad things. He may look as though butter wouldn't melt in his mouth, but I wouldn't trust him. To look at her you'd think that butter wouldn't melt in her mouth. You wouldn't dream she'd even heard language like that. Note: You can also say that butter wouldn't melt. Mums and dads who see their sweet little Sally Ann tripping off for a night's studying at the chemistry society, looking like butter wouldn't melt, would be advised to look closer.
See also: butter, melt, mouth

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