If I was a ghost I would haunt the follwing people: Paris Hilton, The Kardashians, all The Real Housewives, anyone who is racist, is a child molester, an animal abuser, or if they are ungreatful, whiners/adults who are big cry babies, everyone who works at IGN with the exception of Jessica Chobot, and people who show no sign of respect to anyone.
As for what I'll do, I think all I would do is try to scare some people or if I really hate their guts (Like Paris Hilton or the first 3 groups of people that I listed) then I would take control of a few objects and almost end their pathetic and useless lives (I wouldn't kill them, just almost kill them.).