#2. Sumner Redstone and David Geffen

After Redstone's Viacom purchased Geffen's Dreamworks Studios in 2006 for $1.6 billion, there should have been peace in moguldom. Dreamworks, the studio founded by Geffen, Steven Spielberg and Jeffrey Katzenberg, delivered a string of hits — Dreamgirls, Blades of Glory, Transformers — and Viacom's Paramount Pictures ably marketed and distributed them. But Dreamworks execs, reportedly experiencing sellers' remorse, felt Paramount was taking credit for their successes. High-net-worth backbiting ensued. Things really got ugly when a Viacom exec told investors that losing Spielberg would be "completely immaterial" to his corporation. It may sound mild, but in Hollywood this is tantamount to calling Mother Teresa a little bit loose.