My old nan was enthusiastically describing an octopus she'd seen at an aquarium once, and came out with "you should have seen the size of his testicles!"
"Butter wouldn't melt in his/her mouth", or the more usual abbreviated "butter wouldn't melt" is a saying I have never quite understood. People seem to use it when they see a picture of someone or something apparently "cute" - often someones BAYBEE or something. But surely it implies a coldness...