At about 19:48 of the 1st episode of 5-toubun no Hanayome ∬, after Uesugi found out the culprit, he put the test paper on Ichika's head.
Is it socially acceptable to put something over/on other's head in Japan?
I think this might show a sense of superiority in most cultures. At least in where I live (not Japan), it's generally badly offensive to do this except the case of (grand)parents patting their children. As this post says:
Any touching in Japan is very rare among adults, bordering on creepy and/or extremely rude, but teenagers often do it to show their affection, especially friends who are the same gender. If you're both adults I think it's creepy for him to touch your head and you should probably avoid him, but if you're teenagers it's likely to be a sign that he likes you and/or considers you to be a close friend.
Since Uesugi didn't intend to show his love nor feel closed to the quints, there is no good reason for him to do so.
Is this supposed to be a hint that Uesugi is socially inept?