So two AIDS infected gay Black guys walk into Auschwitz on September 11th. The elderly former Kapo by the front gate throws his arms up and proclaims, "Hey, you guys can't stand there!"
The first AIDS infected gay Black guys yells back, "Why? Because we're Black?"
The Kapo shakes his head and says, "No. Of course not!"
The second AIDS infected gay Black guy then asks, "So then is it because we're gay and have AIDS?"
The Kapo shakes his head again and puts his hand to his forehead in frustration.
"Ugh, of course not." he replies. "I don't care who you are or what diseases you have, but you can't stand right there. That's where I buried Anne Frank."
See, you really can joke about anything...problem is that jokes are usually unfunny. Like that one.
As far as 9-11 being a no-no, South Park and The Family Guy went there. Gilbert Gottfried did a horrible joke about 9-11 just a couple weeks after it happened. Hell, Gilbert made Greg Giraldo jokes on Facebook the day after Greg died.
The majority of people will defend or accept any joke as long as it's good.