'I'd been about to say "having a fag out the window",' and I wink at her, and she looks at me understandingly, and pats my hand to show me how proud she is of me not saying that. I smile to myself. I have done well. I will not be asked to leave this time round. I will be causing no scenes.

And then a lady sits down next to us carrying her lovely, blond-haired, blue-eyed baby. He smiles at me, and I make the silly face I make at little children, and he giggles. I am doing so well today, I think.

The lady - an actress - talks to us as she feeds him blueberries. I stop listening to the conversation as I watch him ravenously push blueberry after blueberry into his little face. He polishes them all off, and then starts to swing his right arm about, because he wants more, but his mum's not listening, because she's talking to my wife about car alarms, and the baby keeps on swinging his arm, and then I notice he's got a tiny, square piece of blueberry skin stuck to his top lip, just under his nose, and as he swings and swings and looks grumpier and grumpier, the little black square stays put, and then I laugh very loudly, and everyone stops what they're doing, and I forget myself and I say, 'Your baby looks just like Hitler!'

I smile broadly.

My wife closes her eyes.

I stop smiling.

THE RULES

It struck me, just a few days ago, how many rules I have inadvertently applied to my life. Rules I did not know I had. Rules I did not know I needed.

It happened as I was walking past McDonald's, and there it was: a bright and giant poster of a perfectly formed Big Mac, its light American cheese in the first few glorious seconds of melting, its lettuce crisp and bright and green, its tomatoes dappled by health-inducing dew.

Big Macs are amazing, I thought to myself. Look at that!

I stared at its huge, confident goodness. At its three-part sesame-seeded bun. At the sexy hint of special Big Mac sauce, revealing only a moment of itself, flirting with me, willing me in. And then, as my tastebuds began to stir, and my tummy rumbled in anticipation, I tore myself away, and I strode on down the street.

No, I thought. No Big Macs for you. It's a Tuesday. And you had those Chicken McNuggets on Friday. At least one week must pass between individual McDonald's. You know that.

At the corner, moments later, and holding a dry and wilting hummus and pepper sandwich with organic fennel wheat-free bread, I passed my local.