British, very informal, American, very informal

someone who is always trying to seem more clever than everyone else in a way that is annoying.

OK, smart-arse, do you have a better idea?

• you can bet your life
• you can kiss goodbye
• you can kiss something goodbye
• You can lead a horse to water.
• You can lead a horse to water but you can't make him drink.
• You can lead a horse to water but you can't make it drink.
• you can say that again
• You can say that again!
• You can talk!
• You can't judge a book by its cover.
• You can't keep a good man down.
• You can't keep a good woman down.
• You can't make an omelette without breaking eggs.
• You can't make a silk purse out of a sow's ear.
• You can't make bricks without straw.
• you can't miss it
• You can't say fairer than that.
• You can't teach an old dog new tricks.
• You can't win 'em all.
• you could cut the atmosphere with a knife
• You could have heard a pin drop.
• You could have knocked me down with a feather!
• You could have knocked me over with a feather!
• you could hear a pin drop
• you couldn't have asked for anything more