He's a couple of cans short of a 6-pack
He's as queer as a $3 bill
When pigs fly
If a frog had wings, he wouldn't bump his ass hopping
More fun than a barrel of monkeys (wtf is that really supposed to mean?)
Is the Pope Catholic?
Go piss up a rope (aka Go piss into the wind)
He is so ugly that his mama had to tie a porkchop to his neck just to get the dog to play with him.
I know more, but these are the only ones I can think of right now (mercifully!)