The bizarre Instagram post of Rob Kardashian, who's been battling weight gain, which compared sister Kim Kardashian to a psychotic murderer from "Gone Girl" was only meant to be a joke.

A source told People that Rob Kardashian has a "funny sense of humor" since he "posts weird things and then deletes them. It's just him."

The whole controversy started with Rob Kardashian posting a photo of Rosamund Pike on his Instagram, along with the caption, "This is my sister kim , the bitch from Gone Girl..."

One fan noted, "he got a problem with her? Lol xD."

Another commented, "should we be concerned?"

And still another fan added that she's waiting for a tell-all book from Rob Kardashian regarding the family.

An insider told E! News that Rob Kardashian is "just being crazy and he thinks it's funny."

"He can just be a little bizarre with his humor," the source added.

According to the source by People, the Kardashians-even Kanye West's wife-are not "particularly bothered or insulated" by Rob Kardashian's Instagram post.

However, some of the family members are getting more worried about Rob Kardashian's weight gain.

"He's been depressed and just a bit off in general. But he has always been this way. He just can't lose the weight and he doesn't try - he just sits around," the source added.

Rob Kardashian just celebrated his 28^th birthday and allegedly, he only invited select family members to celebrate with him. Since the weight gain, the sock mogul has been reportedly hiding in Khloe Kardashian's house.

An article from E! claimed that Rob Kardashian just doesn't have the motivation to do something about his weight gain.

"He just doesn't seem to care right now. He's not motivated," the article said, adding that "he seems really sad about his weight, but he also isn't trying to do anything about it."