There is a customer - lets call her Penny - that always bring her own cup, and starts of gentle and subtle in her communication before stepping it up during the payment stage with complaining about "last time took so long"... okay, I'll make a head start whilst she pays, as she sounds like trouble, the sort of customer that just doesn't leave and enjoys being the centre of attention whether you make the drink wrong or not. Milk poured into pitcher...

Ahh... she has wandered off without making any attempt to pay, practically glued to the hand-off area and continuing the charade of being wronged on a past visit. Internal eye-roll. With no attempt of pretending to pay, it is obvious at this point it is all a ploy to bag a free drink. 
She seems anxious, nothing seems to be happening. I'm enjoying the eye interaction between the next customer in the queue and Penny, she has clocked it too, no payment made and unlike some others that have a card prop to seem believable, she sprinted to the collection area.

So.. customers waiting. I have to go back to the Till, with the own cup... and call her across to make payment. She is protesting at needing to pay and it takes a further few minutes for that payment to be complete. I forgot to mention this drink was just a flat white, it has now been 6-7 minutes with no espresso shot poured.
Didn't I say always earlier? I spoke to colleagues about this customer and she was well known of always trying that! Penny doesn't give eye contact, the next time she came in on my shift obviously not remembering me despite being only a couple of days later... the same entire script again, word for word. This time a bigger queue behind her, I was more assertive asking her to pay before I left the till. Order and flat white all done in a minute. 
Never seen her since, the game is up... I'm paid so trimming 6 minutes off silly transactions may seem irrelevant but it does help other queuing customers with quicker service.