Dear Mary: Do I grass on my son’s schoolfriend?

Q. My son was invited, both verbally and via Facebook, to a schoolfriend’s 16th birthday party. However, when I met the girl’s parents at school and thanked them they said, ‘Oh, doesn’t he know he’s been culled?’ They said they had to be away during that exeat, so they’d told the girl to cull the numbers right back and just have a dinner for ten with takeaway pizzas and Netflix. Now my son says the girl has told everyone (150 people) to come anyway. She says it’s the only date everyone’s free before exams start and it will ‘ruin her life’ if she can’t have it. Besides the parents won’t know. How can I alert them that their house is about to be trashed without my son being implicated as the grass?
— Name and address withheld

A. Supply the social editor of a glossy magazine with the name and contact details of the mother so she can ask permission to cover this momentous event which she has heard (from an anonymous source, obviously) will feature 150 of the coolest teenagers in town.