"Well, what do you expect if you work in corporate finance?" I comment, but secretly I'm worried. Jane is the sort of feisty bird who eats patronising twits for breakfast, and could probably fell trees with one well-aimed blow from her razor-sharp tongue.
It's unlike her to be upset by something so trivial, but she's asked for her usual "v&t" without the "t", so something's bothering her.
She sighs heavily. "There's more," she says. And so there is, unfortunately: a whole lot more. Because Jonathan has taken a shine to Jane - and he's not taking no for an answer.
"I've told him I'm not interested, but he just smiles at me in a really creepy way," Jane says and shudders.
"Honestly, I'll go insane if he makes another comment about how attractive I look today, or how I should wear that shade of lipstick more often.
"And if he pats me on the knee again... Do you think I should complain to someone?"
Always a tricky one, this. If she says something to personnel and they have a word with him, he could make her life a misery. Whistle-blowers get short shrift in pretty much any business, and the City's no exception.
On the other hand, Jonathan's clearly determined to treat my best friend as his next merger and acquisition and, as far as she's concerned, his is a hostile bid.
"Well, I think you have to compain," I say. "You know the score. If you fancy them, it's flirting. If you don't, it's sexual harassment.
"If he tries to block your career, you've got him over a barrel."
"He'd probably like that," Jane replies and looks faintly sick. "Urgh, what a thought." Then we both stare into our glasses and I wonder why the world of work has to be so complicated and whether I shouldn't have a neat vodka, too.
Suddenly the idea of us both throwing in the towel and opening a flower shop together seems irresistibly attractive, until I remember that that would probably mean the two of us getting up even earlier than we do now.
Luckily, sexual harassment is something I haven't had to deal with, unless you count the ghastly Neil scheming to get me sacked because I wouldn't go out with him - which, come to think of it, you should.
Still, he never patted my knee and he never made a lunge, except on one occasion after a particularly rowdy business dinner, but luckily he was so drunk by that time he was seeing double and went for the wrong one of me.
So I'm full of sympathy for Jane. The next time I speak to her, though, she's back to her old self and the boss problem is completely cured.
I'm longing to hear what happened to change the situation so, and Jane laughs. "I was having birthday drinks for Toby in Rupert Street at the weekend: just me and 10 terribly camp gay men. Anyway, who should I spot in a corner but Jonathan - with a tight white T-shirt and his arm draped round a beautiful boy."
"You mean..." I say. "Yes," Jane continues. "All that heavy-handed flirting is a cover-up. You know what the City's like. He's terrified someone might find out he's not straight, and ends up overcompensating massively."
There's a relief, I think. Jane can relax at work, and the tonic water industry gets a reprieve.
"Oh, and there's one more thing," Jane says. "I got my promotion."