Inbreeders.
IIRC, Guiliani’s (yes, the mayor of NYC) first wife was his first cousin. He later got an annulment on the grounds that he didn’t know they were first cousins, he thought they were second cousins (still an EWWWWW in my book).
Of course, it’s rumored that he really got rid of her because he wanted to marry his second wife (the one he is currently divorcing), and the first cousin thing was just an excuse.