Can anything be funny, or are some things off limits?
I am pretty sure that the answer to that question is the existence of another question "Too soon?" That simple question proves that there are certain topics that only become funny after a certain amount of time when the pain has worn off and the underlying ridiculousness can be appreciated. I have heard that phrase a few times from stand up comedians when they, I suppose, are testing the waters to see how the audience responds and the "Too soon?" gives these comedians a graceful out,if you will, to go onto safer ground.
Another area that I think is off limits is when a pratfall injures the person. I happily watch "America's Funniest Home Videos" because I know that they won't ever show videos where the people have been seriously hurt, their pride probably bruised, but not their physical person. I laugh only because being the biggest klutz in this family, I empathize with the person falling and it is only by the luck of the universe, that I have yet to be video taped in any of my most awkward moments. I laugh at myself the longest and the loudest because I can only imagine how funny it must be to others and that cracks me up every single time. I can't help it and the more I try to squelch it, the harder the laughter comes, until tears are streaming down my face and I can't talk or barely breath, it borders on the pitiful.
laurieanichols 
Not pitiful at all – cathartic 🙂
that’s a much better word for it 😀
I hate it when I think of a gag “too soon” and have to suppress it. It shows me how shallow I am. Then it’s annoying when you see the gag on twitter and you think “I thought of that!”
There has been a lot of discussion about inappropriate humour in Scotland recently – at the Edinburgh festival there was a backlash against comedians doing “ironic” jokes about rape. The people do not see the funny side at all, quite rightly. It is good that the tide has turned now on that one!
I know what you mean when you see something get recognized and you thought of it first, unrecognizd brilliance argh!. There are some things that just never should be associated with humor and I agree with you, rape is definitely one of them.