Charmless people and things fail to please or captivate interest. They lack appeal and beauty and seem boring, dull, and plain.
Something charmless lacks popular appeal: a joke without a punchline, a plain outfit, a lonely street in a remote town. Someone charmless lacks social and personal appeal: they’re not considered well-mannered, interesting, or, well, charming! But there’s a problem with this unappealing adjective: it’s almost always based on someone’s opinion so it’s personal and biased even. Maybe that plain outfit isn’t charmless after all, maybe it’s just a matter of perspective.