Queuing in my local bookshop a few years ago, I was standing behind some German exchange students, probably about sixteen or so. One of the lads said something in German to one of his friends, and the group all laughed. One of the ladies at the counter said something back to him in German, and the lad went crimson, and his friends all looked very embarrassed, and left the shop as quickly as they could when served.
I asked the lady at the till what the exchange was, and she said that the boy had said that if the fat-arsed biddy on the till got a move on, they would be out of there a bit quicker. She then said that she had said to him "If you would like to wait your turn, I am serving as fast as I can ..." effortlessly embarrassing him totally by making it clear that she had understood the remark intended only for his friends' amusement.
I was impressed!!!