Bad manners.
The child ceases to use many "adult" words, his speech becomes rude. He wants to dress and brush his hair like other guys. Walking with an untied tie and laces becomes as important as for some adults wearing party badges at political rallies. He can forget about manners at the table, sit down with dirty hands, pick his plate and talk with his mouth full. He can kick the table leg with an absent kind. He always throws his coat on the floor. Slams the door or leaves it open. Unaware of this, he achieves three goals at the same time. He changes the role model according to his age. He declares his right to be independent of his parents. And at the same time, he reconciles with his conscience, because he does not do anything wrong from the moral point of view.
These "bad manners" and "bad habits" can upset parents. They imagine that the child has forgotten everything that they so diligently taught him. In fact, all this proves that he learned the basics of good behavior - otherwise he would not have rebelled against them. When he achieves independence, everything that he was taught will return. Meanwhile, understanding parents can be comforted by the fact that their child develops normally.
I do not want to say that at this age every child becomes a bully or mischief. If the child has a good relationship with the parents, and the parents are sociable and receptive people, there will not be a riot, at least outwardly. It will manifest itself when the child thinks that they are encroaching on his independence. Girls usually exhibit this property less than boys. But if you look closely, then they will notice a change in behavior.
What to do in this case? After all, the child still needs to wash and dress elegantly on Sundays. On some of his annoying actions you can close your eyes, but in important matters must insist on their own. When you ask him to wash his hands, say a careless, self-evident tone. It is the edifying tone, teachings and orders that irritate him and make him more stubborn.