When you are really convinced that you are right.
cashier: $24.95 ma'am.
old jewish lady: what? that's supposed to be $19.95.
cashier: it says $24.95 ma'am.
old jewish lady: I want to speak to your manager!
cashier: you want to speak to my manager?
old jewish lady; DATS RIGHT! I want to speak to your manager.
cashier: okay, hold on.
old jewish lady: DATS RIGHT. you're wrong young man.