-No joke in itself is off-limits.
-There is a lot of subject matter that is off-limits to many audiences.
-It is, however, the role of the comedian to test these limits, and outright challenge them.
-Going beyond the limit is a risk. Go for it, but know that your audience may not appreciate hearing about a subject at all.
-Onision gives me the creeps.
-Making a joke about something 'you should know better' about has a chance of backfiring. For example, doing a basic 'Huh, women should stay in the kitchen amirite?' joke just isn't going to get you any respect, at least unless you have it tied to some other element of humor or self-reference - which is something that Internet memes often succeed at, to the point of having women themselves make those jokes.
-What may sound funny now, may ruin you later, or at least be seen as problematic. But what may ruin you now, may become even massively popular later, or at least largely tolerated.
Most jokes are not off-limits to me, unless they illustrate a clear maliciousness towards others. (NOTE: Maliciousness does not = targeted. I'm all for people/types of people being targeted, as long as it is not with a malicious flavor.)
@Cheech - I've found that a lot of things that are close to home that I'm internally sensitive about, I am very able to joke about. This includes some rather dour things. But I've also not had some of the most traumatic things like rape, kidnapping, brutality, etc happen to me, so that's not something I can assume others will be good with.
I'm not very much for trigger warnings. Or rather, I think that once they gained steam, they became very overused. No one should publicly 'speak on eggshells'. I have nothing against the concept in itself, and I do something similar (though I don't use the specific code of 'Trigger Warning' before saying something).