I'm looking for a few good answers here, because this has never made much sense to me.
When is it socially acceptable to make light of a macabre incident? When is it not?

How long is long enough before you can socially make fun of something macabre? How massive does the scale have to be for it to just not count anymore?

Is it okay to make fun of people dying if it's just a number but not okay if they have a name?

I had a bunch of examples on here, but there's no possible way I could use any of them without this being closed. Why do I know this? It doesn't make any sense.

How soon is too soon? How personal is too personal? How many vices does a person have to have to make their death a joke? How much virtue to prevent ridicule?

I really hope you all know what I'm trying to ask, but I really can't be more specific without crossing one of these invisible lines. I think there's one example I can use without offending, but I still don't know why I might think that.

Why can some people say "lol a zombie just ate a man's face last week... teehee" but they can't talk like that about other stuff?

What is this invisible fence that everyone seems to ride so well?

i think south park covered this issue

Right, it doesn't make sense. As such, it can't really explained in sensible terms.

You just have to be socially aware enough to know. I can't even begin to explain it without giving a course on human psychology. You just have to know the audience you're dealing with, the person you're dealing with, the nature of the death in question, and a bunch of other factors and weigh them against how funny your joke is.

If you don't just know already, then I'd suggest staying away from it all the time. Or going for it all the time. Your call.

It's only acceptable to make fun of someone's death directly after the fact if you have a witty pun. Otherwise I would say a week.

well if it was someone doing something really dumb to begin with it tends to be okay to make fun of it much quicker like people eating bath salts then peoples faces. though the people believing in zombie apocolypse might help that one out.
big tragedies are generally not okay to touch for a good few years sometimes decades

It's never too soon for me to make light of something horrible.

But I guess if we're being socially 'correct', it can take a century or more depending on the incident. At least long enough for those alive at the time to have passed away, but ideally long enough to say "humans were less civilized back then and didn't know any better, so it's okay to take the incident lightly".

I think it depends on the person. Some people are more sensitive, and some people have a sense of humor.

My father passed way almost ten years ago now, and anyone tries to make a joke about that will be met with unkind force. Just saying, sometimes no amount of time is acceptable to make jokes, witty pun or not.

As for things that do not directly affect you or the person(s) involved in the conversation, that depends on the people involved. Someone might be okay with making jokes about the Miami attack last month, while another person in that conversation will still be offended by any remarks that attempt to make light of the situation.

26 hours and 47 minutes after the incident - minimum. On a weekday. Full moon.

Depends on who I'm sharing (or not sharing) the joke with.

I was thinking about famous people, or someone that someone has no connection to, it's completely different when it's family.

Gotcha. You might want to clarify that next time though. Still though, that all depends on those involved in the conversation.