My solution for little nazi's is to indicate to them in no uncertain terms that their lack of manners is not appreciated and that I expect an apology forthwith or the manager will have the issue in front of him/her within a couple of seconds. For some reason checkout people seem to be in the forefront of this. If there is a big problem with no apology forthcoming I would loudly call out for the manager and demand an apology on the spot. If that doesn't work then an email to the home office is very effective.