Gibson said that he rejected the role of Maximus in Ridley Scott's Gladiator simply because he felt that he was too old to play the role. He was only 43, by the way. Russell Crowe got offered the part instead, and he left a much more important mark on history than Mel Gibson ever could.
Sandra Bernhard, Sex and the City
Sara Bernhard does not regret passing up the role of Miranda Hobbes in Sex and the City. In an interview with Howard Stern, Hobbes relayed that the script was "terrible" and the pay was just as bad.