Hi kayclan.
I'm glad this did not escalate. I can see how it would be frustrating. I used to get caught up in those conversations all the time. They drove me bonkers!
So I don't do any more defending, simply leave it with an ok/aha! I won't be surprised if she herself brings up the cup scenario again.
Good you don't defend anymore. And I agree, she probably will bring it up again... let her.
I think choosing your battles, or asking yourself "is this the hill I want to die on" is good!
What do you think would happen if you just said, "It does not matter how often it may or may not happen... I don't want it to happen at all. Please use a coaster from now on"? And then drop it.
thoughts?