Amazingly, it would appear from today's Grauniad, David Cameron does not understand the expression 'to coin a phrase':
Cameron defended the change. "I am asking a very sensible and serious question," he said. "I think it is much better to have one organisation in the party which has one mind and, to coin a phrase, we are all in it together."
If he really did say that, then shame on Eton for leaving him unable to distinguish between quoting a phrase and coining one - ie, originating/coming up with one for the first time.