A common interstate aspersion on the internet is to refer to the natives of one state to be "inbred." This is particularly likely to be made regarding the Deep South or Appalachian states.
But what are the facts? No really hard data. But all states specify that marriage between siblings in prohibited. But what about cousin marriages? Here's a map taken from Wikipedia.
Red states specifically prohibit cousins from marrying.
Dark red states make their doing so a criminal offense.
Pink states ban them from doing so, but with exceptions, such as being older, or infertile.
Dark blue states allow them to do so.
Light blue states allow them with restrictions or exceptions.
Think of those incestous New Yorkers or Californians when someone accuses people from your state of being inbred.