Your parents were uneducated, stupid, toothless hillbillies.
@previous (C)
It is a comma placed at the end of a list before "and [final item]". It is correct because it disambiguates between singular and composite list items.
Consider, for example, a list of flavour options in a menu: "plain, spicy, sweet and sour". Since there is no comma before "and", this should definitely be interpreted as 3 options:
- plain
- spicy
- sweet & sour
If there were a comma before "and", this would definitely mean 4 options:
- slain
- spicy
- sweet
- sour