I think jm was serious toothe way Jimin pushed Jin away , i guess he wasn't joking:
On a vlive from about 2 years ago it was sg,jyn and jm and they were doing one of those dancing games
Anyway jm had his controller in his hand and jyn kept insisting that it was actually his controller despite jm saying that the controller was his and finally jm turned to jyn and asked him if he was still a child ,with the way he was behaving over the controller
Jyn then told jm thay he needed to get his mind right
Also why is jyn always with older men? Always famous older men at that...sponsers I suppose