Rich and I stare deep into our coffees, hoping for all the world that we're not next on his agenda of shouting and madness.

Now the man is giggling insanely and swatting imaginary flies away from his face, as he bothers an elderly woman drinking tea on her own. He sits down next to her and begins to rant about Tibet, just inches from her face. She stands and leaves.

'That poor woman,' I say. 'We could have saved her from that man.'

'Yes,' replies Rich. 'We could have been heroes!'

We watch the man pacing around, looking for someone else to shout at. Two French students with backpacks and maps approach and take a seat, oblivious to what's going on. The man homes in on them.

'Oh no!' I say. 'Rich! He's going for the French!'

The man begins shouting in their faces.

'There's no such thing as a free lunch!' he's shouting, laughing almost uncontrollably after each time he says it. 'There's no such thing as a free lunch, is there?'

'This is terrible, Rich,' I say. 'Imagine the impression these poor students will get of our proud and noble country! They will think we consist only of shouting men who wander around dashing all hopes of free lunches!'

'We should intervene,' says Rich. 'But how do we do it without attracting his attentions ourselves? I don't want to spend ninety minutes learning that there's no such thing as a free lunch.'

Now the man is doing squat-thrusts in front of the students. He jumps to his feet, and shouts, 'See? Exercise? The students don't really know how to react, and smile politely. They clearly need to escape. But how?

'Quick!' I say. 'I've got an idea! We can offer them an out!'

'How do you mean?' says Rich.

'I mean, you speak a bit of French! You could go inside, go to the toilet, and then come out again as if you're part of their group! You could tell them they're welcome to join us over here! It would be like code!'

'Yes,' says Rich. 'That's an excellent plan. We will be heroes!' 'Heroes!' I say, and we clink our cups of coffee together.

Rich leaves it a moment, and then gets up to go.

'All I need to do is look confident and talk loudly,' he says. 'Wish me luck!'

'Bon chance!' I say, and in he goes.

This will be great, I think to myself. It will be an important moment. A chance to show that not all Brits are as loud and odd as this man. That these Frenchmen are welcome here. That we are polite enough to know their language, and will use it to rescue our European brothers. We are heroes, I think.