Well, this is a gross simplification in many cases, but okay, I'll play:
-Avatar (cartoon): When Korra gets her powers back through DEM.
-Command and Conquer: The moment I started playing Tiberian Twilight.
-Merlin: The ending. Oh god the ending!
-Red vs. Blue: Season 10, episode 10. The moment when the dark path season 7 set the series on finally caught up with me, and I declared "screw it, I'm done."
-Resident Evil: Where in Resident Evil 5 you engage in a turret section against el gigante, after a previous turret section of shooting at ganados on motorbikes.
-Sonic the Hedgehog: Where I was introduced to the boost mechanic in Unleashed, where the concept of 'earning speed' went out the window.
-Star Fox: Command. Just Command.
-Star Wars: The Force Awakens.
-The Walking Dead: Season 5 in general
-Warcraft: When the series transistioned to MMO format.
-Warhammer Fantasy Battle: When the whole setting was gutted.
That said, like I said, this is an oversimplification. Of the ones listed, the only one that I can really say is completely dead to me is Red vs. Blue, whereas some franchises had the courtesy to die at the end of their run (Command and Conquer, Warhammer, Merlin, etc.) I mean, still watch the Sonic Boom cartoon, still keep up with Warcraft lore, etc.