Rob had been silent on social media for several weeks and seemed to be making an effort to avoid the public eye, which made the aggressive post all the more surprising.
"He's been depressed and just a bit off in general" one insider tells People magazine, adding that the main cause of Rob's malaise is his ballooning weight.
"He can't lose the weight and he doesn't try," says the source. "He just sits around."
Rob made headlines last May when he bailed on Kim's wedding at the last minute, reportedly to avoid media attention and negative comments about his weight.
The anonymous insider concedes that the Kardashians are concerned about Rob's health and mental state, but claims that the Gone Girl post has been treated as a joke amongst family members.
"He has a funny sense of humor and posts weird things and then deletes them," says the source. "It's just him."
It's true that Rob has a long history of publicly making jokes at his sisters' expense, but it's worth noting that in this instance, Rob has not deleted the post, and it's currently been favorited nearly 100,000 times.
He's also deleted all of his previous posts and unfollowed everyone...including his family members.
