Best thing to do is get in the queue in front of a load of pensioners,and just faff about, taking ages to put stuff on the belt, taking endless time to ensure that all bar codes are not visible, nothing must be piled on anything else, or even within 2 to 3 inches of the next item.
Then when it comes to pay, fiddle with your pockets, and say loudly im sure i brought some cash with me, then get a card out, and loudly chant the number which is your year of birth,finally put all the accumulated bags in the trolley one by one SLOWLY,finally when you think all those behind have aged enough, slowly move away from the checkout, then STOP DEAD,look puzzled and loudly ask the checkout operator, you diod give me the receipt, or card back didnt you .
Furtive scuttling of the checkout operator, as thy search for missing card ,receipt etc.
As you finally look back youll find various pensioners in a state of catatonic shock or just given up the will to live, some of the more militant ones will be looking at various items with which to inflict grevious bodily harm on you, a french stick or cucumber can inflict terrible injuries on an un prepared shopper.