How I Met Your Mother — "Last Forever" (2014)

How I Met Your Mother's finale destroys nine seasons of emotional buildup by killing the Mother off-screen and reuniting Ted with Robin, undoing a decade of character growth. The twist lowered its IMDb rating to 6.9, a 35% drop from the series average of 8.3. This reversal of narrative trajectory outperforms #4 in betrayal of audience investment, as it invalidates 208 episodes of storytelling.