What do to? Friend needs me for a blind date (double date) but I know it's a fat girl!?

Ok here is my dilemma my friend Richard is going out with this hot smoking stunning girl Esmeralda, BUT, Esmeralda will not go out with him unless he finds a date for her friend Vanessa. Vanessa is a really fat and smelly girl and has a little bit of a mustache growing in. They want to do a double date, this guy is my best friend and has asked me to do it but I don't want to get stuck with the fattie while he is off with a girl who looks good enough to win the prom queen next year. i dont want it to dampen our friendship, but i cannot bring myself to go out with this girl.