I say drop him, and if he doesn't like that, sell him.
Undignified childish nonsense like that whilst representing The Arsenal football club? Unacceptable.
Saturday was a skidmark in the underpants of our great history; a stain which can only be washed away with the soap of sacrifice.
I believe that the standard managerial response to these incidents used to be 'You want your player to be disappointed when he's substituted. It shows he's got desire', followed by an explanation that you were worried about a groin niggle/midweek fixture he had and didn't want to take any chances.