what it would be?
For me, it would be Christmas cards. They're so much hassle to write and get sent off, people get all worried if they get a card from someone they forgot to send one to, people who no longer have any real contact or interest in each other anymore are afraid to be the first one to break the habit of sending cards etc etc etc
I think it would take a lot of the stress out of Christmas if this tradition ceased or was confined to people you are still in touch with but do not see on a regular basis. So no cards to neighbours, siblings who live down the road, couple you met on holidays 15 years ago and wouldn't recognise if you fell over them in the street......