Will Smith goes on stage at the Oscars and hits Chris Rock then verbally threatens him from his seat

Joke or not.....make light of something about my wife she can't control in front of me would most likely earn more than a slap to the face.
They are in Hollywood at the Oscars where "roasting" is expected. If you can't handle the roasting, stay home. JK Simmons was basically called old and ugly. As an old and ugly person, I could see how he could be offended by that joke. He took it in stride.

If someone comes out of the blue and insults your wife, I can understand you being angry. This isn't out of the blue. He and his wife are front and center at a "roast-type" event.

Finally, I think Smith's actions are insulting toward his wife. Jada Pinkett Smith is not anyone who I think is unable to stand up for herself. She looks like a strong and independent woman who could go up and do the slapping. If anyone had the right to slap (not saying there is), it belonged to her--not Will Smith...who actually laughed at the joke initially.