#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.
R-Truth wanted to 'kill' former WWE writer. More details HERE
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.