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

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 alone with the fattie while he is boinking 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. I know it sounds like I'm being mean but this girl seriously weighs about 240 pounds (according to the girls in her gym cl). she's a junior and i am not kidding about the mustache thing she has more facial hair than me.