The empty tin cans of butter cookies that are kept to store unrelated items, such as pencils and pens. Invariably opened with the expectation of cookies, the result is disappointment.
I thought there were some cookies left but it turned out to be a disappointment box.
n. A mailbox belonging to a college student (usually checked on a regular basis) which he or she normally finds empty, and thus a disappointment.
"Hey, hold on a sec, I've gotta check my disappointment box...yep, empty as usual."