If only I hadn’t dropped my pen, I could have avoided the whole unsettling incident. But it slipped out of my notebook as I made my way back to the office and bounced onto the pavement.

A nice passer-by picked it up, and gave it back. I thanked him and thought nothing of it.

I was in a rush anyway and didn’t factor in that it was odd that he was obviously in a rush as well and that we were proceeding at the same pace past Oxford train station. And then outside Domino’s he tapped me on the shoulder and asked if I could help him.

“Of course.” One good turn deserving another and similar cliches were racing across my mind.

He was probably lost and needed to catch a train or bus.

“I don’t want to offend or upset you though,” he said. Vague alarm bells started ringing.

“What can I do to help,” I asked, and as I looked at his face it suddenly occurred to me that if he was a fruitcake, he could attack me there and then and there would be nothing I could do about it. I scanned his face for possible clues.

He was thin, with a beard and a woolly hat, but well dressed and not obviously dirty, smelly or high on anything.

He seemed clean and neat.

“Knee,” he said intently.

“I’m sorry?” I asked thinking I’d misheard him.

“Knee,” he said again. “I’m sorry though I don’t want to upset you or anything.”

“I don’t understand,” I tried one last time.

“I want you to knee me, as if in self defence,” he said seriously.

I nearly asked him where and how. Did he want me to kick him in the groin?

And then a loud voice in my head said: “Walk away and keep walking” and I told him I was just going to leave him right there and to stay where he was.

And I left him standing on the pavement.

As I strode off, head snapping back to make sure he wasn’t following me, I wondered if he’d recorded it or somehow filmed the whole incident. Whether he’d replay it later with his mates and they’d all laugh their heads off. Whether this was part of some new comedy show, some sort of reality trap, or whether he was just severely delusional and mentally deranged.

Whether he was dangerous or not, who knows. I didn’t wait around to find out. But it has made me think about the thin lines that exist between winding someone up and endangering them. And why Mark Watson felt totally within his rights to write a piece in The New Statesman recently, calling for boundaries to be put in place for comedians.

Because it seems that anything goes now. Like Frankie Boyle’s intolerant rants.

Whatever, it was a sobering and surreal experience and one that made me, a random woman minding her own business on the way back to the office, vulnerable.

A rather serious column this week then, but to be honest I’m rather unsettled by the whole experience.

It was like someone walking over your grave.