It's rude to yell at someone for what ever reason.
John is shopping for groceries and finishes up, and is now checking out when the cashier hands him his change which is a dollar less than he's owed.
John wants to let the cashier know they made a mistake.
John mentions that the cashier forgot to give him the extra dollar they owed him.
John loudly exclaims that the cashier was trying to shortchange him on purpose.
The cashier apologizes for their mistake, and vows to be more careful in the future.
The cashier is really embarrassed and suffers significant anxiety around other customers from then on.