From Getlucky12341, Tales From Retail:
I was training a new cashier on a register, mainly just standing there incase the trainee had a question, when this mother came in with some groceries and her kids.
She says that she needs us to look up her store credit card, and I inform her that our store doesn't do that and that she's probably confusing us with another store.
Lady: "Well you've done it before so figure it out."
I offer to get a manager, and she says that the store has never had the ability to search for the store credit cards. This angers the dummy and causes her her her to say "Don't lie to me, you've done it before" before leaving her groceries on the belt and walking away.