In a series of tweets and Instagram posts, Ellin criticised the King Richard star for his response to Rock’s joke about Jada Pinkett Smith’s bald head.
Ellin wrote on Twitter: “Can’t believe anyone would defend Will. Gas lighting narcissist who made entire night about himself.”
The comedy writer added: “All about Will. All anyone will remember. An overly sensitive out of control bully.”
He also criticised Smith for taking the focus away from other winners: “Not Questlove’s amazing speech, not the deaf actor from Coda who was awesome.”
Ellin – who is currently creating a TV show with Charlie Sheen – added: “They would have shot Jesse Plemons if he did the same thing.”
He also questioned whether Smith should have been thrown out of the ceremony: “Should Will not be escorted out? Arrested? Is this some type of special treatment?”
The Men in Black star has since apologised for his behaviour, stating that he was “out of line”.
Smith said: “My behaviour at last night’s Academy Awards was unacceptable and inexcusable. Jokes at my expense are a part of the job, but a joke about Jada’s medical condition was too much for me to bear and I reacted emotionally.”
Smith’s reaction has also been criticised by Alan Davies, Mia Farrow, and Judd Apatow.