I had to remind my kids that while they are showing good manners, the person didn't ask them to do it, they did it on their own accord. So if the person thanks then it is fine, but we shouldn't expect it.
Excellent life lesson. A hard one, but we should all do the kind thing even when the recipient is a jerk. I always tell myself (when I do something nice for those jerks) that just maybe it will change the sort of day they're having and they will do something nice for someone else. Probably doesn't happen often, but surely on occasion.
susie