#2 Honky Tonk Man and Bret Hart
Honky Tonk Man is one of the most bitter people in wrestling, and this is on the public record. However, he seems to have a considerable beef with the Hitman Bret Hart.
Nearly everyone knows about the infamous Montreal Screwjob, and how Bret was angry with Shawn Michaels for nearly ten years. However, not many know about his backstage beef with Honky Tonk Man.
It seems that Honky Tonk Man's waning years in the WWE were spent slacking off and not working hard in the ring--at least according to Bret Hart. He once told Honky Tonk Man 'You don't hit me hard enough,' ripping on his ability to work snug.
Honky Tonk Man blames Bret Hart for his WWE career ending, believing that Hart used his influence with Vince McMahon to cost Honky his job. We don't know if this is true or not, but the animosity between the two men is genuine enough.