Chances are it would have flopped, but one of the first things that came to mind for me was Ted DiBiase during The Legacy days. Orton was bullying him around, possibly slapped him and they teased Ted was going to lay him out and the fans were right behind it.
I think it woulda flopped. Did they LIKE him or did they just hate Orton? Because when Riley turned on Miz they didn't LIKE him, they just hated Miz...and he disappeared after his angle with Miz was done.
As minor as it is, I think Santino should be a heel. It's fine that he's comedic relief, but it's more fun laughing at him than 'laughing with him' when he's a face.
I can think of a bunch of people who are in there wrong roles and were turned poorly, but nobody else that hasn't been mentioned in this thread had the missed opportunity recently. And Cena should have turned with nexus, not mania. Mania was always about the passing of the torch. Nexus was way over, and if Cena was the mouthpiece it could have been big.