This is not the first time Sale has had an issue with the ownership and management of the team. It's easy to blame the player, but I think management has to be in for its own share. A normal person does not get angry enough to slash his own jersey in a normal situation. So either Sale is toxic, or the situation in which he finds himself is so unbearable that the one last issue over the terrible jerseys causes him to lash out.
Worth mentioning -- the jersey in particular is absolutely AWFUL, easily one of the worst and weirdest in the history of MLB. I mean they don't even look like baseball jerseys at all. Most of the time when you see a throwback jersey the size, weight and shape are still conformed to what the athlete is used to. This one, I don't see how it can be, because of the presence of that godawful collar
http://www.dailyherald.com/storyimage/DA/20150827/sports/150828845/AR/0/AR-150828845.jpg&updated=201508272319&MaxW=800&maxH=800&noborder
As habit bound and set in their ways as ace pitchers sometimes HAVE to be, I can understand chafing under the gimmicky jerseys, which weren't popular with players even when they weren't "throwback." Throw in the evidence that the relations between players and management were already tainted due to the Drake LaRoche fiasco and the failure of communication that took place during that crisis, which fed a feeling that the White Sox ownership has no idea what it's doing and more interest in cashing in than in trying to win baseball games, and I think you begin to see why Sale would act out in this way. It was still massively immature, but there's a lot of environmental factors in play as well.