The Star Wars Holiday Special
Heavily promoted and given a prime-time slot on a Friday night in a world starved for more Star Wars, The Star Wars Holiday Special unfolds on CBS, enveloping millions of viewers in the slowly-dawning horror that the promise of a new adventure for Luke, Han and friends has lured them into watching a third-rate variety show, albeit one in which the character of Boba Fett makes his first appearance. George Lucas disowns the Holiday Special almost immediately, and it is never allowed to be repeated again. 
Hear about it on the Sci-Fi 5 podcast