Re: Butter wouldn't melt in her mouth.

i have only heard (and used it) to mean someone is very cold. but i can see how it could be used to define a bald faced liar..

another one we used at home was 'drinking vinegar' as in have you been drinking vinegar?-- and it was used when some one made a very cutting or nasty remark about something.

it was not interchangable with being a sour puss, but was specifically used for the idea of sharp, cutting remarks.