I ordered a coffee and made a joke. It happens. In this case, the other customer in the queue was amused where the girl serving wasn't:

Her: That'll be £2 please.
Me: [hands over the money]
[pause]
Her: Right. £2. Ooh yeah, you already paid.
Me: Well, I know I paid you pretty well, but I think in this case a lap of honour wouldn't be appropriate.

In the lift after this moderate exchange of Ashley-silliness, the other patron said the he felt she didn't appreciate my sarcastic wit. I said I wasn't being sarcastic. I was being sardonic. I like a nice bit of sardonic. I suspect that it means the same. But my word is better.