People who, while shopping, block an entire isle by parking their buggy on one side while they browse through product on the other making it impossible for other people to pass. Or, people who decided a group meeting in the middle of an isle, blocking the path of other customers, is an okay thing to do. Have some courtesy, move your conversations off to the side so people can get by and when browsing through product, make sure you're not making it impossible for other people to get by. How selfish can these people be?