Wiktionary
just plain folks
n. (alternative form of just folks English)
Usage examples of "just plain folks".
The painful fascination of pressing your cold little nose against the windowpane and deciding that rich is nasty, virtue is just plain folks and the American Way.
He made it clear that he wasn't any scientist, but just plain folks, standing here, humble before this great new wonder of the world, and that he was here because American plain folks had chosen him to represent them at occasions like this, and that, looking at this modern miracle, he was overcome with a feeling of deep reverence and humility and gratitude .
If they were normal ARVN, I think they'd just shoot some civilians and steal their clothes and pretend to be just plain folks.