So I buzzed through Arkham Asylum and started up my playthrough of Arkham City.... such a good game. But I encountered something really weird yesterday (7/4).
In the basement of the courthouse is a man in his cell called "Calendar Man". I approached him and he started talking about having bombs to set off to get him free and how that would be appropriate for Independence Day. And some more 4th of July references after that.

Basically, he does that for every big holiday. Just a weird coincidence my first interaction with him in the game was on a holiday.