Chideltjen is a screenname I have on another board. It's not greek, so I've been referred to as Chid for short.
I've also heard "Chie" rather than "Kai." I actually a friend say "you don't pronounce chinese food 'Kai-neese food.'"
ETA: for the letters themselves... I've heard we're the X triangle sorority or the X-Change sorority. (Joke for all the math majors out there...)