The Simpsons are to air their 500th episode which is nothing short of astonishing for an animated show in prime time. The Simpson's have been around for more than two decades and have provided so many memorable lines, sayings and gags. Last year the show came within an eyelash of being cancelled. Every episode begins with Bart at Ms. Krabappel's Chalkboard. Bart has written more than 288 memorable quotes on the chalkboard including, "The Good Humor man can only be pushed so far" and "The world may end in 2012, but this show won't". Look below to see all of Bart's chalkboard quotes.