Unless you are an avid collector, Batman underwear is probably not something you would buy for yourself. This is more something that you would get as a gift. Some superhero underwear comes with a cape attached to the back. I’m guessing this is not the most comfortable thing to wear, but that is not really the point. The idea is that it is a fun thing to give or to get, and have a laugh over.
I find these hilarious:
Batman underwear for men: bioworld Batman Caped Black Boxer Briefs