Your missing the point. This guy thinks he has a choice about when to be a dictator and when not to. I hope it is not true, but depending on who he has around him and who is in control of Congress, he might be right.
So let's imagine he decides to be a dictator, only on day one. But then 100 days into his administration things are not going exactly the way he wants, so he decides to have another day where he is a dictator. And then the news media criticism him for being a dictator, do he decides to be a dictator again and several people in the media just disappear. Oh and then there are protests, but he knows how to deal with that, another dictator day. And on it goes.
And even if you really think he was telling a joke, you still have to understand that if he was telling a joke he was doing it to avoid answering a question.
Imagine you are running for President. And an interviewer asks "If you win election, do you have any plans of abusing your power?". That is not a hard question, that is a softball of all softball questions. You shouldn't even have to think about it. You say "No, I would never ever do that!".
Not what Trump said.