> A complete stranger who has nothing whatsoever to do with you, who has never tried to do anything for you, nor has been expected to, has never disappointed you. They've also never failed to disappoint you, because they have not failed in any regard whatsoever.

Nobody who uses the phrase ever means it in this way. The point of using the statement is to convey that you are familiar with the person’s history.

As another commenter has already pointed out, “has never failed to disappoint” is not the same statement as “never fails to disappoint”. The habitual present can’t refer to empty sets, as it is only used to refer to repeated actions.