It's an excuse to go out on a weeknight
All that roleplay gives people an excuse to meet someone who’s not their type, unless you’re dressed as Batman, because Batman is everyone’s type. And there’s no such thing as too busy to celebrate -- again, unless you’re Batman, because Batman is very busy.
Nobody wants to celebrate Halloween on Nov. 1st. So if it falls on a weeknight, by golly, you are going out tonight! Much like the Batman you pretend to be, you will patrol the city looking for costumed weirdoes. Although in your case it ends with you guys raising a beer to each other, which is a happier ending all around.
...has Batman ever tried that? Maybe his friendship is all the Joker's been after this entire time.