You are an investigator. You are to investigate The Joker to know on which day he usually goes on a date with Harley Quinn. The Inspector said that The Joker is lying if and only if it's Monday, Tuesday, Thursday, or Friday (hereby, telling the truth on other days). The Inspector is telling the truth.
You: Well... I hear that you always lie on Monday, Tuesday, Thursday, and Friday; other than those days*... you always tell the truth. Is that correct?
The Joker: Nope, that's not true.
You: Oh, interesting...
The Joker: I was lying yesterday. I... uh...
You: Umm... yea?
The Joker: ...
You: Hmm, are you fine?
The Joker: Tomorrow I'll also lie.
You: Hmm... I see... So the day after tomorrow you'll also lie?
The Joker: Yes I will.
You: And I suppose you were lying yesterday?
The Joker: Yep.
You: Well... Apparently, I already know that today is the day you usually go on a date with Dr. Quinn every week. Poor you to find yourself in this prison today.
The Joker: ...
You: Based on your expression, I can tell that it is indeed today. Thanks a lot Mr. Joker.
So, on which day The Joker usually going on a date?