7. Aunt May
Aunt May died of a heart defect during the Clone Saga story arc. Her resurrection is not only one the worst in comics history but also one of the most convoluted and confusing. It involved a clone, Spider-Man and Mary Jane's "baby", and Norman Osborn returning from the dead after nearly 20 years.
The reason Aunt May's time had come was that Peter no longer needed that figure in his life and the writers were struggling to come up with ways to keep her around and, more importantly, keep her relevant. Since her return from the dead, May has become a perennial plot device. She serves little to no purpose beyond being a weight around Peter's neck, keeping him trapped in this strange space between adolescence and manhood, despite how subsequent writers have chosen to portray him.
Aunt May has long since stopped being a character in her own right and has become a crutch for lazy writing. She was even the cornerstone of One More Day, arguably the most despised event in the history of Marvel comics.