For me, it’s the context rather than the subject. I would never tell a joke that I thought would offend someone or hurt their feelings. A joke that I might tell one friend would never be said in front of another.
To answer the OP - none, there is no subject I can’t handle. There are a lot I don’t find funny , but I can still handle them.
Of course, if they’re just a setup for a bad pun, someone will have to die afterwards. But that doesn’t mean I won’t enjoy the joke. 
(All the usual yadda, yadda about context, racists telling racist jokes, etc. fits here)
I completely agree. Other “hot buttons” for me are practical jokes - I too sympathize with the victim.
Other things that I put in that category are just general rude and disrespectful comments - sometimes jokes/comments are appropriate (if, for example, you’re hanging out with your frat brothers), and sometimes, depending on whether or not you’re in mixed company, they’re rude, objectionable, tacky, uncalled for, and frankly, disrespectful.
Upon preview, what Hypno-Toad said. 
I need to stop reading this thread right now, b/c the temptation to make references to horrible jokes is amazing.
But I sort of agree on a mix of what Rigamarole and Sarahfeena are saying. It’s technically OK to make fun of whatever you like, but it’s still ok for someone else to be offended by it. That’s a freedom we should have too.
-Tokio
“That’s a pretty big word for a…nah. nevermind.”