I was reading this article on Buzzfeed about ridiculous questions that people have asked on Yahoo Answers about underwear. The last question was this:
Tis an interesting answer, and I wonder if it could be found anywhere in the canon? Any comic geeks out there know the answer, or can perhaps propose a better one?
But why stop at Batman. What does Superman wear? Does the Flash go commando? I reckon the Green Lantern wears briefs. I wonder if Wonder Woman wears a wonder bra?
No way, as Bruce Wayne, like his bat brethren, his boys like to hang so he goes commando.
Going commando while wearing a tight-fitting ballistic rated combat suit? I don't think so. He undoubtedly wears some sort of microfiber protective brief, possibly something with D3o impact gel.
Considering that most incarnations have him wearing BRIEFS outside his tights, I think the answer is clear…
If a woman wears tight pants and she doesn't have a slip mark pressed through the fabric on her ass, she wears a thong.
Superheroes wear tight pants and don't have any slip marks, so (in my opinion) they wear thongs or nothing at all.
They also make no-show panties without stitching that will not show up under tight clothing.
the bat-thong!