The only thing worse than adding a cash shop...
...is people whining endlessly about how a cash shop for purely cosmetic items is THE WORST THING EVER TO HAPPEN IN THE HISTORY OF VIDEO GAMES.
Well, that and 1.0. 1.0 was also worse.
EDIT: And everything that happened involving Wildstar.
Honestly, there's a lot of stuff that's worse, but I felt like limiting myself to stuff involving MMOs for purposes of defining "worst".
EDIT 2: Also City of Heroes getting shut down. That was much worse.
As was that time I tried to create three HQ Isolator Components before getting a crafting class to 50.
And that time I got banned from the beta forums for suggesting that someone commit suicide in protest of Fire II not being named Firaga. Although that was less "worse" and more "still worth it". Holy hell...yeah, that garbage parade was also worse.