Having jumped ship from the nWo and WCW, Sean Waltman in his X-Pac guise was underdog personified within the Degeneration X ranks. So his partnership with the equally misunderstood Kane was a heartwarming mismatch... while it lasted.
Eventually, however, X-Pac destroyed the whole relationship by turning heel on his former best friend. Not only that, but he pretty much stole The Big Red Machine's girlfriend Tori at the same time. The fact that Tori was fully complicit in this act made this a screw job twice-fold. Kane would ultimately have to dish out two lots of revenge in the final segments of the feud, to reconcile what was in essence, two heel turns.
In the weeks leading up to this, X-Pac would subject Kane to all kinds of physical and mental torture, and in joining the Triple-H-sanctioned dark side of DX, exposed an impressively nasty streak to his own persona. It was arguably one of the best angles of his WWE career.
He also damn near blew Kane's face off with a flamethrower in an episode of Smackdown.