When my sister was in college, she was hanging out with friends one night, and a member of the group decided to tell what they thought was an entertaining anecdote. But the punchline landed with a resounding thud, leaving everyone unamused.
Another friend looked at the storyteller and said dryly, "Next time you tell a story like that, you should end it with '...and then I found five dollars.'"
Of course, this was just his snarky way of admonishing people to give their listeners at least something interesting to take away from a tale. But it truly is a great shorthand way to acknowledge with a wink that a joke didn't work or that an anecdote was, in fact, unremarkable.
Basically, it can be used anytime you don't get the response you'd hoped for. Alternatively, you can ask it as a question if you're on the receiving end of a snoozer conversation: "... and then you found five dollars?"
My sister and I now use the phrase regularly, and some friends have added it to their repertoire as well. I'd encourage anyone to incorporate it whenever possible, with one rule: you can't adjust it for inflation. Because the only thing more boring than stumbling upon such a small amount of money is that story you just told.