According to Dante Alighieri's Divine Comedy there are several different circles of hell, each reserved for a particular type of sinner. What do you have to do to wind up on the Pac-Man circle? Blinky reveals the truth.
There are many different theories about how the ghosts in Namco's classic arcade game found themselves in the unfortunate undead state. I'd like to think that they were each young musicians with promising futures and hot girlfriends that found themselves at the wrong end of some sort of yellow disc creature gang territory conflict. Their girlfriends died horribly, followed by the ghosts themselves, and then a crow brought them back to life for vengeance.
Or maybe they just died trying to masturbate with a belt around their necks. One of those.