Explanations/etymology also appreciated!
For Joe Shmoe, it means a very average or below average person. It’s a derivation of the practice of using “shm-” to dismiss something (eg “Practice shmactice. We’re already perfect”).
And “John Smith” is meant to be the most average name or person imaginable, so they have the “most common” (citation needed) first and last name as well.
In Norway we have the stereotypical Norwegians “Ola Nordmann” and “Kari Nordmann”. Ola and Kari were quite common names a couple generations ago (not so common now). “Nordmann” literally translates to “Norwegian [person]”, but is also a not-too-uncommon last name.
We typically talk about them if we’re describing something or some situation and what the stereotypical Norwegian would do/think.