For The Birds

Explanation:  If you tell someone that something is for the birds, you are telling them that you think something is worthless or ridiculous.

Example:  Jasper was convinced there was buried treasure in the old mine somewhere, but his wife told him he was wasting his time, and that his attempts to find the treasure were for the birds.

Origin: This phrase is of American origin. It is US Army slang and originated towards the end of WWII. Here is an early example of its use from his piece from The Lowell Sun, October 1944:

“Don’t take too seriously this belief that we have football at Camp Ellis solely for the entertainment of the personnel – that’s strictly for the birds. The army is a winner… the army likes to win – that’s the most fortunate thing in the world for America.”