How to mess up a relationship? How long have you got? I mean, there are the really obvious things, like unashamedly using his underpants as a handkerchief or encouraging his obsession with Wikipedia by asking questions that take a full day involving diagrams to answer (“How did JFK get such a bad back?”). I also find chirruping “this is my famous...” before plonking a plate of something new in front of him doesn’t go down well, either. It’s also inadvisable ever to form the sentence “I’m a bit mad” — but please start using “don’t nag me” 50 times a day from very early in the relationship, hence undermining the concept of nagging. Never suggest his hair is unlikely to obtain the perfection of Michael Portillo’s, and, crucially, never drink your own urine — even if a naturopath tells you it will stop your suicide-inducing hay fever. In fact, never mention the word naturopath. But you know all this. More important, avoid the following:

1 Sulking for anything longer than four years

Don’t let an unimportant disagreement over Jack Nicholson balloon into a war of attrition that consumes the latter half of your twenties, blinding you to the nice things. I remember lying in bed on holiday in Wales when my then boyfriend came upstairs and asked if I was going to come up a mountain with everybody. No, I said, certainly not — everything in our life is going to pot, see? He shrugged. He looked very handsome at that moment — he was lovely, actually — and I felt myself wavering, then I noticed he had a computer monitor tied to his waist. One of the old ones, the size of a television. I said, WTF? Oh, we’re doing some filming, he said — something to do with getting our host’s children to attack him as if he were an Orc who worked in IT. Now who could resist a nutter doing something like that? Moi. I just lay there and read Penelope Fitzgerald for the next 18 months in a nonspecific huff. That’s the thing about sulking: it’s just acting, and as such it is addictive and can kill.

2 Committing to someone before you have met all their brothers

The sibling rule is absolute and cannot be broken. There is always a younger/older brother who is more attractive, and you will sit there on Christmas mornings for the rest of your life mentally locked on to the little patch of flesh visible beneath his shirt. One time I was standing in a hall with a boyfriend when his brother walked in. This brother was beyond fit. A man with a wild look in his eyes usually sported only by stuntmen. All Legends of the Fall-type hell ensued. (The boyfriend: “Are you actually trying to go out with my little brother?” Me: “Define your terms.”)

3 Forgetting to pace yourself

Since it’s particularly irritating to men when a woman necks 15 units in two hours and is asleep by 9.30pm, it is helpful to extend the scenario to the whole relationship. Going in too hard only means that any subsequent and entirely normal shift in temperature will feel like a terrible falling-away. I once had a boyfriend who I love-bombed to such a degree it was ridiculous. I can remember him sitting in a beer garden, blinking, as I gossiped away and threw back my head laughing. It suddenly struck me that he could have been a cardboard cut-out. That the fun I was having here was the fun of hanging out with myself being fabulous. That I was really being incredibly weird. To keep stoking a relationship into an all-consuming full throttle is to step on a treadmill: it is aerobic, but will never actually take you anywhere. Do not fear light and shade. Be braver all round. And shut up.

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