as cunning as a very cunning fox that has just become professor of cunning at cunning university (off 'Blackadder' the telly programme)

and

as camp as a row of tents

made me laugh out loud!

This is a great thread - I'm enjoying it so much!

From Tennessee Williams - and not as funny as the above:

as nervous as a cat on a hot tin roof
(or was it "as restless as"? - that somehow makes more sense)