Someone who will say one thing that sounds good, but when it comes to actually doing it, does the opposite.
Comes from Nick "Dick" Clegg's campaign in which he said how he will help Britain if he becomes PM ands when he did he backstabbed everyone who voted for him(namely in raising university fees).
Guy 1: i promise to keep university fees down.
Guy 2: got my vote and your in power. nice to keep fees at £3000
Guy 1: thanks, although i've just put fees up to £9000
Guy 2: You're such a clegger