Silver tongue is an expression used to describe a person who has a clever way with words. Add some clever sarcasm, or sleazy lies to this person's attitude, and there you have your silver tongued devil.
I honestly can't believe I'm making a bible reference, but this is what Google gave up for silver tongued devil:
"When Satan with his silver-tongue approached Eve, using the serpent as a mouthpiece, note that the very first thing he did was to question the veracity of God’s spoken word. Paraphrasing, Satan said to Eve, ‘Has God said you shall surely die if you disobey? God has not told you the truth. You will not surely die, for God knows, though he has not told you, that in the day you eat the forbidden fruit your eyes will be opened and you yourselves shall be as God, and you will know good and evil, that is, be able to decide for yourselves what is right and what is wrong."(Gen. 3:1-5)
by Krazeder September 17, 2014
Someone whom likes or the act of eating old hairy, gray, old lady puss.
Luke is a silver tongue devil.

Oh man I would love to give her the the silver tongue devil right after I kick in her back door.
by Meatdrapes July 4, 2010