Yoongi always played cool with him. He could transform in a goof ball just for him in a matter of seconds. This was their intimacy. This was Yoongi showing him a part of himself he does not show often. 
Little things like squishing his cheeks would often get him in a annoyed mood but somehow when Jungkook did it he couldn't help but smile. 
The kid was so cute. Much to Yoongi's pleasure. He had big teeth and loved plain white tees so Yoongi made sure to write a song about it.