I was constantly short changing people at work, my mind just goes blank sometimes. Most of them would say something even if it was just a penny. If it was over 20p I'd probably say something but I don't actually check my change that much. I've probably been hustled out of quite a lot in clubs etc where it's too loud to hear the bar person so I just hand over a bunch of change and walk away. Suppose that's my own fault though
