butter wouldn't melt in one's mouth

(redirected from look as if butter wouldn't 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