To be upset over something that cannot be fixed, often something minor. Please calm down, you're just crying over spilt milk. We already submitted the report, so we can't fix it now. A: "Why is Hannah so upset?" B: "Oh, she's just crying over spilt milk. She just fell down and ripped her stockings—she'll be fine."

Don't be upset over something that cannot be fixed. Said especially of something trivial or minor. Oh, honey, you just ripped your stockings a little. You'll be fine—don't cry over spilled milk. Don't go crying over spilled milk. We already submitted the report, so we can't fix it now.