It is extremely awkward when adults behave in a childish way.
I’m sure you’ve all looked at someone being thoroughly selfish, unable to cope with getting their own way, and thought to yourself: “How childish!”
I’m sure you’ve all also got drawn into some petty squabble or other. Something on the same level as who’s got more than their fair share of the back seat of the car. I know I have.
From time to time, we all behave like children.