It's also for yet another almighty row with Boy Three.
"A B C D E F L M N O P X Y Z," he trills jauntily. Then stops: "Where's Q. I missed Q. It's my favorite. Quickly queen."
Sensing the volume of our outing was about to rise with his dropping mood. I quickly volunteered. "A B C D E F G H I J K..."
"It's jai, not jay," he said.
"Actually it's jay."
"Nooo. Miss C says it's jai."
Seeing trouble ahead at the idea that the omniscient Miss C might be under threat I explained: "Well some people say jai and some people say jay. They're both right and it's important to know that."
Too late. Very loud wail: "It's jai. You're wrong."
Sigh.
We live in the West of Scotland and it's true there's a linguistic quirk that many people do say jai (to rhyme with fly) instead of jay (to rhyme with pay). It causes a little minor bafflement but everyone I've ever met understands both words.
I understand that no one should have to abandon the things that they grew up with, that are part of their culture and region for a homogeneous and bland UK neutral version.
But Miss C, if you're reading, please can you explain to your pupils - many of whom have none-west of Scotland parents - that there is an alternative. In any case, they'll need to know if they're going to leave home and spell out loud at the same time.
Out for lunch in Glasgow just before things got saucy over a letter.