for the birds, it's/that's

for the birds, it's/that's

It’s useless, worthless; not to be taken seriously. This slangy Americanism dates from the first half of the twentieth century and crossed the Atlantic after World War II. One writer suggests it alludes to droppings left by the horses of horse-drawn carriages, from which small birds would extract the seeds. If this source is correct, the expression is a euphemism for “horseshit.”