I know this is a throwaway joke, but I was interested anyway...

According to my own local Markdown formatters, the answer would be both "usr" and "bin", with the surrounding slashes removed, but the internal slash remaining. In other words:

usr/bin

(but underlined instead of italic!)

Of course, this problem is nothing new since a filename might easily be named `_my_file_`.

Same as in my_snake_case_name :)