It's a mild insult which I picked up from me Pops. Whenever someone didn't do what he said he was going to do, Dad would later refer to him as 'the potlikker'. He might pluralize it to 'potlikkers' if it involved more than one person.
The only thing is, I can't find where the term is even a vague insult. My online search has come up with 'pot liquor', or how you can make liquor in a pot, or 'potlikker' which is apparently some kind of southern United States soup delicacy. Either way, I can't see where it's particularly degrading.
Yet I've added the term to my repertoire. Why not? It was good enough for Pops and doesn't appear to be actually hurtful. So put that in your pipes and smoke it, you potlikkers out there.