Randall hasn’t bothered to name any of them so the community has given them unofficial nicknames.
Megan is actually named in multiple comics though, so is Danish (Black Hat's girlfrenemy) (actually that was picked semi-arbitrarily by the community). Cueballs also have different names occasionally but they're all drawn the same.
And actually I do believe that certain non-named characters are the same comic-to-comic. Black hat and Beret guy almost certainly are.