E.g. the checkout guy in our local supermarket who was deliberately, provocatively rude to me the other day for no reason. Can't be bothered to describe everything he did but it was pointed and deliberate and there was no reason for it. He doesn't know me. He even made a show of being over-the-top friendly to the woman behind me who seemed a bit confused at all the attention 
I normally shrug off stuff like that but he was so obvious about it I couldn't help feeling angry. I still smiled at the bugger out of habit! I didn't know whether to complain about him, laugh in his face, ignore him, wish him a nice day? I could see how much he was enjoying being rude and I thought afterwards if that gives him kicks he probably has much bigger problems BUT at the same time I didn't deserve to be treated rudely. I'm nice! And I'm still a bit annoyed.
Tellingly his was the only empty queue and he's been a bit off before so I think he's a nob in general but had decided to turn the full beam of his nobbishness on me that day.
So wise MNers, how do YOU deal with people like this, bearing in mind it's my closest shop and I'm in a lot and I will have to see him again? Should I have a pithy comeback at the ready?