Help me out find the reason why this is rejected

 Or maybe her hand?.. 

By @Geisard

You mean her arm. The arm needs to be out of rubber for getting to this pose.

Other issues with the woman: the teeth and lips:

The nose and the confetti with this “chromatic aberration”.

The eyes with those strange wrinkles:

The “strange” change in texture:

And btw also the washed out structures around the eyes. They look like there was excessive noise reduction and sharpening applied.

The hair:

Changing over to the man's hair, the background, the texture of the hair and the background, and broken hair flying around:

The nose and the confetti:

Lower teeth are missing (you could argue that you see the tongue, but it still looks strange. To the right, there is a bad tooth.

The right part of his mouth (his left) is strangely straight.

Artefacts on his jacket, the collar disappears:

(1) white outline

(2) strange change of light

(3) what is this?

(4) very hard line for out of focus elements:

I'll stop here, I could find more of the errors if I looked on.

First and foremost, the hand. So you're correct on that issue. But there are numerous areas that need cleaning up that become apparent when viewed at 100%. The teeth look off as well. Lots of "dust spotting" is also needed. The confetting on the bow tie makes the tie look poorly rendered. I'd remove the confetting covering her teeth as well.