Mommy613; Don’t worry! Believe me, he didn’t just decide to buy a pair of jeans
on his own. Knowing that this is not the kind of upbringing he had.
He most probably has a friend, or two in Yeshiva who bought/wear them too, and he
is just trying to fit in. I am not getting into the right & wrong of this. I’m saying this is more his friends, and yeshivah, where he most probably picked it up from.
Maybe the Yeshiva isn’t the type you thought it was, or this is an isolated incident
within the yeshiva. Either way you should confront him in a respectful way,
not bossing him, rather suggesting this isn’t the way he was brought up,
or the the way you want him to be. However making a big deal about it, or commanding him to stop, without his input, or him feeling it was your decision not his,
will not bear positive results.