"Vanity working on a weak head produces every sort of mischief." Mr. Knightley; Emma
When my son was a teenager I suspect there were a lot of adult persons who would gladly have waved this particular quote at him and accused him of just such weak headedness. Their definition of "mischief" was often a lot more broad and dire than mine or his father's. Most teenaged boys tend to be somewhat vain, and it is a good thing to a point, or they would collapse under the stress placed upon the teens of the past couple of decades. Vanity is often just a coping mechanism it seems to me for boys....and girls....and men.....and women.
Sometimes the mischief created by teenaged vanity seems inappropriate to adults, who have far more life experience and have developed the ability to predict consequences for their actions that teenagers simply haven't yet. For adults to be able to discern the difference between teenaged mischief and real trouble making, they sometimes have to be able to put aside their personal fears and definitions of what constitutes appropriate teenaged behaviour in order to look more deeply into a situation, being prepared to put up with some minor irritations while the simple mischief makers learn their lessons by suffering their own consequences on the way to future maturity.
It is a tough call sometimes for parents, for any adult, to decide what teenaged behaviour needs to be ignored, and what needs to be discussed, and what needs to be stopped before someone is seriously hurt in some way.
And now my vain, weakheaded son is in New York doing a Masters Degree. And his vain, weakheaded mother is so pleased that he survived all her mistakes in discernment in his younger days.
"It is very unfair to judge of anybody's conduct without an intimate knowledge of their situation."
Emma Woodhouse; Emma