'Wait, wait...I've forgotten my voucher.'
'Well, can I pay for all this now, come back another day with the voucher and refund me the difference?'
'Sorry, vouchers are not refundable.'
'But your manager said we can work this out the other day.'
'No, sorry you would have to come back later with the voucher, if you want to purchase all this today.'
Stupid Customer (Angry)
'Oh really!? So you are organising my day for me now are you?!'