Clearly the greatest joy of being a doctor is when your friends start asking you for help with their vile medical problems. Last week, for example, the woman I have loved unrequitedly for more than a year asked about a lump in her breast. Oh joy, I thought, as she described in detail the soft, fluctuant mass just lateral to her left nipple.

Of course, this only gets worse now that I am a psychiatrist. My patchy knowledge of physical medicine has already receded, but worse than that, my friends are starting to ask questions about their mental health. Or even more hideously, the suicidal gestures of their partners.

You can see, I would hope, that there are at least eight million reasons why I would want to avoid these questions. The main one is that in most cases there are going to be a whole bunch of intrusive questions that I will need to ask.

I do not, at a party, want to start asking about someone 's bowel habits, nor do I want to start excluding a sexually transmitted disease as the cause of their symptoms in front of their faithful Christian girlfriend. The wisdom of this justification has, I like to imagine, been distilled into my stock response, which I can only recommend all doctors take up.

The conversation goes like this: "Mike, do you know anything about that thing where you get a really sharp, shooting pain across the bottom of your foot when you take your first steps in the morning?" "Hmm," I say, scratching the side of my head. "Do you need a poo?"

It is the best response. It is, for a start, the only strategy which never fails to raise a smile among my puerile and hypochondriacal sisters, and can be deployed for any medical problem. For example, last week on the bus: "Mike, can I talk to you about Sam? He's drinking heavily. He becomes abusive and threatens to kill himself before vomiting everywhere." "Hmm," I reply, scratching my head: "Does he need a poo?" Problem solved.

So, to return to Sophie's breasts: there is no way I am going to sacrifice what little respect and affection she might have for me in the name of some cheap poo gag. No, I'm going to give this one my best shot. I rack my brains for unsexual pathological data on breasts and try to be business-like.

Do you have a first-degree relative with breast cancer? "My mum almost died of breast cancer last year." Bollocks. This was something I had made big mileage out of, to my enormous shame. It wasn't just mileage, obviously. I mean, I'm not that low, and I love this girl as a friend, too. But I had a massive crush, and it was a truly awful scene, and I was in the thick of it: the medical details seemed irrelevant. I never thought forgetting the physical pathology behind it would have such repercussions.

I flounder, trying to swerve us back to the neutrality of fact. "Right," I say, confidently. "Your risk of getting it yourself is 13%." "So what are they going to do at the appointment?" she asked.

"I guess they'll do an FNA." God knows if that's true. "What's an FNA?" "They get a needle and stick it into your breast under ultrasound guidance. Then they suck a bit of the fluid off the lump to see if it's cancer or not." "Great," she says. "Thanks."

"I'm sure it will be fine," I say. I'm probably wrong - about everything. I'm not a doctor. I'm just pretending. It's like those stories in the Sun about impostors with no medical degree. I am just a sad, alcoholic fantasist who tells poo jokes. She starts to finish her drink. "Look! Over there," I blurt. "Didn't he used to go out with Kylie?"