How many Jews does it take to screw a lightbulb ? Hitler wouldn't know
What is the reason behind this kind of joke today?
Nope.  It's just that people think I'm being a jerk when in reality, I was simply trying to make a joke. But it will never be that effective unless you mention Holocaust. I want to make another one so I'll take your comment on Jewish folks this time.
I am sure Hitler asked some Jews to change a light bulb before. I remember reading about him befriending one.