Idea: Sandwich

Subway, or some other sandwichy place.
Customer orders a sandwich, guy behind the counter gives it to him.
C: Hang on, what is this?
G: It's a sandwich.
C: No, it's not. This is two pieces of bread. (Holds them up.)
G: Like I said, a sandwich.
C: A sandwich usually has something in between. What kind of sandwich is this?
G: It's original flavoured.
C: Huh?
G: It's plain. No filling.
The idea is that so many people are allergic to everything nowadays that they have decided not to put anything on sandwiches so no one gets sick. I have no time to write this at the moment, someone want to give it a go?