It's considered taboo to date a cousin.
Jeff is at a family get-together and finds his cousin Beverly very atractive.
Jeff wants to be with his cousin Beverly.
Jeff tells Beverly she is really beautiful, and they should hang out as friends more.
Jeff asks his cousin Beverly on a date and expresses his love for her.
Beverly feels flattered and likes her family more and feels good.
They get married, have kids and the kids are deformed and sick.