#2 Hulk Hogan

Hulk Hogan had an admirable heel turn in WCW and most of his career in WCW he remained a heel and got great success doing that. But in WWE, it was a completely different story.
WWE built up Hulk Hogan as the American dream, an All American who could do no wrong, who was a hero and turning that affable persona into a dastardly heel was a bridge too big. Even during Hogan's stint post WCW when he came back to WWE as a member of the NWO (and a heel) but it only took one match against The Rock for WWE to turn him face again.
The character of "Hollywood Hulk Hogan" was built over the years and it was just too big a thing for the WWE crowd to turn against Hogan and boo him out of the ring. Hulk was always a fan favourite (arguably still is) and could never justifiably get over the crowd as a heel.