When I found that it was real I thought that Smith must have taken offense to a Rock joke about Smith's apparent open marriage with his wife Jada Pinkett Smith. Jada Pinkett Smith has done the do with at least one man not named Will Smith while still being married to Will Smith.
But that wasn't was set Will Smith off last night, although the actress Regina Hall made a joke cracking on the Smith couple for precisely that reason.
No what evidently made Smith so angry that he assaulted Chris Rock was that Chris Rock made a joke claiming that Jada Pinkett Smith was getting ready for a sequel to GI Jane, a film in which the lead actress, Demi Moore, famously shaved her head. Jada Pinkett Smith suffers from alopecia and has apparently decided to keep a buzzcut.