OK well they haven’t quite proven that it’s hereditary, but it does seem like being prone to saying the wrong thing isn’t just bad manners — some just have lower inhibition and can’t help it.
I came across an old article in The Age from January 2005 where some boffins did some tests using a card with “blue” written in red ink on the card, then served up a chicken’s foot under high social pressure (a Chinese lady presenting the chicken foot as her favourite dish) and low social pressure (”here have some of this Chinese food”). The people who didn’t get the blue/red quiz right were also less likely to be inhibited even in the high pressure social situation, and complain about the food.
So next time you make a social faux pas, don’t feel so bad, you’re just a bit defective.