korien_dec20“Oh, by the way, the paint on that bench is wet. Don’t sit on it.”

“Now you tell me! I just sat down!”

We say “now you tell me” (or a variation, such as “now he tells me”) when we receive information just a little too late to be useful. If you warn me that your dog bites, but I have already tried to pet the dog and gotten bitten, I wish that you had told me a little bit sooner.