So last night I was on a tram somewhere, contentedly listening to Radio Lab with my big coat zipped to my chin, when I noticed the little girl pinch her lower lip. She was about twelve or thirteen, sitting diagonally across from me with her dad. She was pretty, but she'd clearly hit the puppy fat stage hard and I felt for her, because being a teenage girl sucks big, hairy balls. She kept catching my eye and pinching her lower lip, and I could tell she and her dad were talking about my lip piercing, which happens sometimes. She pinched her earlobe, then her nose, and while I couldn't hear what they were saying I could tell they were talking about piercings. And she looked relaxed and happy, and her dad looked relaxed and happy, and they were talking quietly, easy and engaged, and then I choked up.

Here's the thing: in times of hormonal normalcy I'm not an especially tearful person. Don't get me wrong, when my uterus gets premenstrual ideas anything will get me going, including, memorably, the Tyra Banks Show, but normally I don't cry very easily. Since implanon has, happily, made me quite barren PMS is no longer an issue.

Here's the other thing: high school was very, very hard for me. It is for many people, but I was an unlikeable introvert with bad acne at a famously catty girls' school. I didn't make it easy for myself. Then, within the space of about 18 months I had to deal with my mother becoming ill with a brain tumour, Rock Eisteddford, my father's death and one hell of an awkward phase. I don't mean to be self-pitying, whatever doesn't kill you etc, but it was a tough time, and on a certain level I never got over it.

So there I was, looking at this girl and her dad, and my eyes welled up. Oh, shit, I thought. Why must I always make a complete arse of myself on public transport? I remembered the time, long ago during the Commonwealth Games, when Chloe told me I had a spider on my knee. I did, and I immediately leapt to my feet, swiping at my knees, squealing 'Get it off! Get it off!' I looked up to see a tram full of grey-haired, horrified Games goers. 'It's okay,' I said loudly. 'I'm not schizophrenic.'

But, you know, when you try not to spontaneously cry on a tram like some kind of overly sentimental crazy person you immediately will, and as big, dumb tears rolled down my cheeks I turned pointedly to the window and tried to wipe them away. When I glanced back up the little girl was looking at me, shame-faced. She must have thought I was crying because they were pointing at my lip piercing. I wanted to get up and tell her it's okay, it's just that I have no dad and I was an awkward teenager, too, and you never get over these things and sometimes they make you cry on a tram like an idiot, but that would have been crazy.

Instead I got off at the next stop and stood there for a moment, feeling the cold night air on my wet cheeks and burning eyes. I took a deep breath and let my old, stale grief speed off down the street with the tram. Then I walked to where I was going, and it only took me a little longer, and when I got there I was fine.