There are people in the world you naturally want to be around or seek out. They are the people who are optimistic and look for the good in the world. They might not be exciting, but they prefer to have fun whenever they can and look for ways to draw other people into their happiness. When told to "have a good day", they respond, "I plan to."
On the other side, there are people you avoid any conversation with or any interaction with at all. Being around them makes you feel sad and tense. If they seek out people, it is to share their misery with them. The same "have a good day" is likely to bring a snort or a list of ways that the day can't possibly be good.
