What's the worst/most disappointing "red herring"

Red herrings often pop up in fiction, be it the "obvious" love interest ended up not being "the one" or the classic the "appearant" bad guys was the good ones all along.

For the most part I don't mind, some changes from the predictable and familiar story is often a good thing.

But not always, be it that you saw it coming a mile away, it was a bit late in the story too swap sides, or you simply would have preferred it the other way