Lunchbag Letdown

A lunchbag letdown occurs when something you had been looking forward to turns out to be far worse than originally anticipated.

The term originates in the lunchroom (be it school or office or otherwise) where after a long hard day someone sits down with their lunchbag hoping for something tasty. Instead they find something unappetizing, whether it be the wrong lunch, it's moldy, it's cold, or any other multitude of problems.

After such a situation, it can be said that your lunchbag was indeed a let down.

Tom: I can't wait for lunch *pulls out lunchbag*

Jim: What do you got?

Tom: Aw man! Tunafish? I HATE Tunafish!

Jim: What a lunchbag letdown.