A fun (and friendly) way to fuck with people:
Go to a drive-through with two windows, one where you pay, one where you pick it up, with plenty of traffic.
You have several options, obviously, but let's choose the one which -confuses- people, rather than ruining anybody's day:
Order a drink. Nothing else. Pay for it. And now drive off without picking it up.
The person behind you pulls up, and is given a drink. Queue confusion. (The reason you order just a drink is so that they know immediately they didn't get their order, and you don't screw over the five people behind you in line by having each one in turn pick up the wrong order and drive off before discovering they have the wrong items.)