How many jews does it take to change a lightbulb? No one knows, lights come on, gas comes out.
What are you implying?
It's a joke about the Jews dying in gas chambers in World War II.
Gassing Jews isn't something you'd wan to joke about. It can easily get you tarred and feathered as anti-Semitic.
Would it had been a better joke if there was a punchline about Hitler?
Maybe using the holocaust as a joke isn't great. A lot of people just find it insensitive and there are many more actually funny topics to joke about.