No, this is not a hoax, Francisco Domingos Joaquim from Angola can open his mouth wide open for 17cm (6.7 inches). He have set a world record of Widest mouth at the Big Mouth competition in Rome . It was measured 17cm which earned him a ''dream come true''  title of Guinness World on the set of Lo Show dei Record in Rome, Italy, on 18 March 2010.

(c) MrRalfJack