saying

[sarahduggan]

waht does " butter wouldn't melt" mean - referring to someone sweet?

[Quizmonster]

Click http://www.worldwidewords.org/qa/qa-but3.htm for an answer.

[Dusky]

It's a shortened version of "he looks as though butter wouldn't melt in his mouth" which is used to describe someone with a false air of innocence.  I think it refers to the fact that, despite being as guilty as sin, the cool, calm appearance wouldn't cause butter to melt...

[Rhesus]

It's a variation on saying somebody is cold-blooded; a person who had cold blood, and therefore a cold mouth, wouldn't melt butter.