my wife does this to me ............... "look how much I've saved you with these bargains" ....which we didn't need anyway
Try asking the checkout girl in Sainsburys if you can just have one of the buy-one-get-one-free items for half price..... it confuses the hell out of them
Best one was when I got a reduced pack of cakes buy-one-get-one-free reduced from £1 to 20p but they only had one left so I said can I get the free one tomorrow...... erm no you can't.... so I said ok just knock the £1 off the bill for the one I haven't got then