i don't think we can ascribe rudeness to teeenagers in this way.
they live in a different world.
some of these comments seem to expect them to operate in the same way as people of our age.
also a true gift should be offered/given with no strings, else it's not really a gift. why should we expect thanks for a gift.
not talking about Op, but someone mentioned people in the church getting married, so not close pals presumably.
give a gift/card if it pleases you to do so; if it then annoys you not to get a thank you, perhaps don;t do it in future.
i read once of the eskimo people, when they lived in igloos.
to leave a gift, they crept up unseen and left it outside. the aim was not to be seen/identified, because unless it was anonymous, it incurred a debt, if only of thanks, and so ceased to be a gift.
this was regarded as bad form, though allowances were made for youngsters; so people would pretend they hadn't seen who left it, until they'd got the hang of it.
i found this idea appealing. anything not a pure gift ie anon, was akin to a commercial transaction, and involved some recompense.
this persists in our culture. i hope the bigwigs across the road don't get us anything for xmas, or we'll have to get them something. this all leads to waste of money and materials.