Being a man of encroaching middle-age and portlitude, last month I was asked to fill in a couple of times as an understudy department store Father Christmas.

Swathed in cheap velour, covered in itchy facial hair and home to a gurgling stream of acrid sweat, it was a magical experience, and one that taught me several important lessons. Lessons about how Father Christmas is making a list of who’s naughty and nice, but he’s making it about the parents. He’s also noticing who’s pushy, who’s overtired, and who’s been drinking heavily.

Father Christmas is judging you, parents. And here’s why.

You haven’t provided a convincing backstory – There are many wonderful tales about Santa Claus. He lives at the North Pole (or in Lapland) and is married (or single, or a large, asexual gnome), and makes all of the toys himself (or with an army of elf-slaves). When your child starts asking questions about the practicalities of being Father Christmas, that’s the point where you jump in and say something like “Well, we thought that Father Christmas did it like this, isn’t that right, Father Christmas?” It’s not your cue to stand mute, check your text messages, or to try to stare Santa out. This is especially true with the question “Are you the real Father Christmas?” which can be answered a number of different ways: “No, Father Christmas is very busy and has lots of helpers;” “Of course I am;” or “How dare you question my authority? You get nothing!” Unless you give SOME HINT as to the way you answered that question, Father Christmas may well end up contradicting you, and I’m pretty sure I know whom your children will consider a more reliable source. Play the game, people.

You’ve brought a toddler, good luck with the nightmares – For many children, meeting Santa is a HUGE deal. It would be like meeting George Clooney, if George Clooney also crept into your room and gave you whatever you wanted… No, scratch that. not like that. Anyway, for young children, this is their getting to meet Madonna, or the Queen, or Stephen Fry, knowing that they’re going to be assessing your behaviour while you do. Also there is a huge beard, music, garish surroundings, and probably an odd smell. There is no excuse for taking a child under 3 to see Santa. They ALL freak out. If you want a picture of a tiny baby with Father Christmas, fine, but to any child who’s vaguely sentient of what’s going on it’s going to be pretty traumatic. Congratulations, you’ve just queued for 45 minutes because you were determined to give your child nightmares.

You’re outsourcing your parenting – If you’re bringing your child just so that Father Christmas can threaten them, you need to take a good, hard look in the mirror. Then punch the mirror and use the shards to slice your own awful face off with. Yes, the promise of presents is part of the whole deal, but telling little Ciaran that Santa probably won’t be bringing him anything when Santa is sitting right there is a dick move.

You are just terrible – If your child asks for Grand Theft Auto V then Father Christmas probably wouldn’t be doing father Christmas’ job if Father Christmas didn’t point out that that’s a game rated 18, and your child is only 9. When he says he probably won’t be bringing that, it doesn’t help if you then add your voice to the pleas to bring it “He has been really good, though.” At this point, Santa reserves the right to think of you as a monstrous cunt. Just so you know. Santa isn’t saying it, but he’s thinking it. And he likes making lists.

You refuse to help your inaudible child – Sometimes it all gets a little much, and the intense emotion that comes with talking to Father Christmas renders some children utterly mute. At this point, you can help, by prompting or answering on their behalf. Anything but playing fucking Angry Birds, while Santa and your child experience a tense, Cold War standoff.

You keep referring to a letter Santa hasn’t seen – Let’s just be clear. The Father Christmas you’re going to get isn’t real. you’re the grown up. That shouldn’t need explaining to you. So when you say, “You remember the letter Lucy sent to you, don’t you, Father Christmas?” That’s fundamentally unhelpful, if there are going to be follow-up questions. And there ALWAYS are. “She really wants that thing she put at the top of the list, Father Christmas.” Fuck you. “It would be especially good if you could remember the instructions she gave you in the PS.” Up your stupid arse. “And of course you’ve remembered the password she wrote in it, so that she’d know she was dealing with the REAL Father Christmas.” May your head be full of the eggs of a false-widow spider, which will burst and flood all over your Christmas dinner, the resulting lack of pressure on your brain will give you a new appreciation of colour, but will also render you incapable of speech or unaided urination. Merry Christmas.

For the children, meeting Father Christmas can be a magical moment. For the adults, remember to be on your best behaviour…