So my partner and I don't socialise much together. It isn't that we dislike each other but rather because we don't really feel the need; I have been watching his back for so long now I can hardly remember what he looks like from the front.
You can choose your friends, but you are stuck with your relations and, in the same way, having a partner is almost as good as having a real friend.
A relationship like this does not even need words any more; we can be both supportive and adversarial (and sometimes without offence) to each other as each case demands.
However, there is still a place for a sporting one-upmanship. Making an obscure diagnosis is all very well but true tactical gratification comes from starting a kid with an obvious minor viral illness on antibiotics after my partner has seen him a few days before and given only good and academically impeccable advice.
By now, of course, the kid is getting better on his own, but the credit will go to me and my astutely prescribed antibiotics, and my local prestige will rise as my partner's correspondingly sags; as La Rochefoucauld observed: 'There is, in the misfortune of one's best friends, something not entirely unpleasant.'
And in my defence, my anecdotal experience is that, contrary to academically impeccable advice, viral illnesses do respond to antibiotics.
Because if I don't do it, and we end up having to refer the kid, as sure as eggs is eggs some smart-alecky junior doctor will start antibiotics (for an 'ear infection' usually) as soon as he hits the hospital doors, while raising an eyebrow just enough for the parents to interpret it as 'is your GP thick or what?' and then both our names will be dragged through the mud.
So I'd rather we screw each other than have the hospital screw both of us; it's always better that these unpleasant things are done by someone you know.