Probably my least favourite storyline would be the one with Kane and Zack Ryder.
Zack Ryder had worked really hard to get himself over and was well placed to be a long reigning and succesful US Champion, but then they had Kane destroy him on a weekly basis till he had no heat remaining, and then they buried him some more.
It was purely done out of spite as he had got over on his own and not through the WWE Machine. WWE wasted a potential future star. The Ryder character was perfect for them as well. Kids liked him because he had a catch phrase and had an outgoing personality. Adults liked him because they appreciated that he'd got over through hard work and hadn't just been handed a push.
And, more than anyone else, nerdy Boys aged 11-15 idolised him because they could live vicariously through him. He was a basic nerd and didn't meet the standard definition of what a "cool" chracter was. Kids like that go to school all the time and feel like outcasts or losers. They'll never connect with someone like The Rck or John Cena because they are larger than life and almost living super men. Zack Ryder was a average guy, with clear nerdy tendancies, but he was succeeding. He was comfortable in his own skin and had got where he was despite not having the same attributes as the other big stars. Those kids would have bought every single piece of Ryder merch they could get their hands on. You just start coming into money around that time as well. These kids would have also grown with Ryder as his character grew, in what would have been an organic progression.
WWE sometimes screw stuff up by being clueless, but this one was pre-meditated. It really started the down turn in my fandom actually