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.