Someone walking into a door, accidentally hitting themselves in the groin, electrocuting themselves,etc.. can all be considered humorous in spite of the potentially serious injury that may occur to said person. Just watch America's Funniest Videos or something, a lot of the humor centers around people doing stupid stuff and breaking something or hurting themselves and we consider it good and fun.
I suppose it depends on the context of why it happens and whats going on that makes it amusing or distressing.
"There is no such thing as spare time, no such thing as down time, no such thing as free time, there is only life time. Go."
― Henry Rollins
If I think/feel that someone has wronged me in some way and they then proceed to fall from grace in some fashion I derive orgasmic amounts of pleasure from their misfortune.
I would expect nothing less from the Thoroughbred of Sin.
"Hey Capa -- We're only stardust." ~ "Sunshine"
“Pleasure to me is wonder—the unexplored, the unexpected, the thing that is hidden and the changeless thing that lurks behind superficial mutability. To trace the remote in the immediate; the eternal in the ephemeral; the past in the present; the infinite in the finite; these are to me the springs of delight and beauty.” ~ H.P. Lovecraft
I think almost everyone experiences it to a certain degree especially if there is an element of "karma", people see others as "undeserving" of something (ex. like the rich), and/or pure jealousy. Or, they plain like it. From a more detached stance, I am starting to think that's why a lot of people watch "reality shows" besides the perceived amount of entertainment.
On the other hand, it can be funny if there is surprising/shocking element to it. I even laugh if I am in physical pain because it diffuses the situation and sometimes how one became hurt can be funny, Others might be doing the same thing. Spinning things in a different way can make almost anything funny.
The sweetest fantasies so often have a nugget of nastiness at their core. When the German poet Heinrich Heine dreamed of the good life, he imagined this: "A humble cottage with a thatched roof, but a good bed, good food, the freshest milk and butter, flowers before my window, and a few fine trees before my door; and if God wants to make my happiness complete, he will grant me the joy of seeing some six or seven of my enemies hanging from those trees."
If it's someone I really don't like, I might get a little pleasure from it for a little while but not for very long. If it's someone I like, then never. If it's someone I am apathetic about, then never as well.