Based on "traveler's checks", I'm going to guess at least a couple decades ago. Cashier probably called 911 because they thought GP was trying to commit fraud with "fake money".

I mean, in what world can you cash travelers cheques at a dairy queen?

It's been a very long time, but my grandmother always used to give me spending money for vacations in the form of Amex traveller's checks. IIRC you could use them in essentially any situation where you could use an ordinary paper check (which was substantially more common back in those days).

Dairy Queen was a favorite from my childhood, I had moved away from Texas years earlier so I decided to indulge while visiting. These days I’m more into Sonic - the food is better, they have a greater variety of sweet treats, and I really like their iOS app.