The café at the London Review Bookshop in the city's Bloomsbury district is the perfect place to meet the humorist (he would approve of the word) Simon Rich. It's a "proper", old-fashioned bookshop where stock is carefully chosen by humans, then sold without the heavy discounting book-buyers have come to expect these days.
Rich, who is perilously thin and wears his thick hair in a Beatles-style mop, knows that where we're sitting is too chi-chi to be anything like an accurate reflection of The World Out There, and understands that "if someone is reading your work in the 21st century, it's really an incredible miracle. There are so many other books; so many other activities". But he'd rather things were different. Not because he's a snob, but because he's drawn as a writer to outmoded literary forms: the "humour piece" and the comic novel.
This may surprise anyone whose knowledge of the 26-year-old New Yorker is limited to the fact that he writes for Saturday Night Live, America's longest-running satirical television show. (He's the youngest writer to have worked on its scripts.) But you can be a hip young gunslinger and a throwback at the same time. "Being an old-fashioned comic novelist is sort of like making top hats or monocles," he admits. "But I can't help it! These are the books I grew up loving. I always wanted to write one."
And so he has. Set in a present-day Manhattan private school, Elliot Allagash is a horribly funny coming-of-age novel about a lonely misfit named Seymour, who becomes the willing pawn of a delinquent classmate: Elliot, the son of America's richest man. Inspired by his father, a paper tycoon who buys brilliant art so that he can have the pleasure of destroying it before anyone else has had a chance to look at it, Elliot likes to use his fortune to implement cruel, manipulative schemes. Mostly, his motive is revenge. But in Seymour's case, it's pure amusement. Can Elliot transform Seymour into the most popular boy in the school? And what will happen when he does?
The plot is nothing special: in outline it suggests Amy Heckerling's film Clueless, itself an updated version of Jane Austen's Emma. But what sets Elliot Allagash apart is the antiquity of its comic brio: you sense at once that it's the work of someone who grew up snorting over Evelyn Waugh.
"It's shamelessly ripped off from all the writers I love," says Rich, "and those are people like Waugh, PG Wodehouse, Roald Dahl, Douglas Adams. Also Terry Southern [author of The Magic Christian and Stanley Kubrick's main collaborator on Dr Strangelove], who wasn't English but wrote in a very English idiom.
"Like them, I like to write premises, and the thing about a premise is there's only so much comedy you can milk out of it. So to write a successful comic novel, you need a character or situation that allows you to pack in a ton of unrelated premises, otherwise you'll end up with a bloated, one-premise book. Novels like Catch 22 and Hitchhiker's Guide to the Galaxy were set in the army and in space so that Joseph Heller and Douglas Adams could digress - which they needed to do to keep the reader's attention.
"In terms of the plot itself, I just went to all those great genie stories - everything from My Fair Lady to Dr Faustus. What happens when you find the lamp? You hope you wish for the right things, but invariably you don't.
"Simple plots are good. If you read Candide, there's no plot. Well, there is, but it's minimal. If the plot is too complicated, the reader's brain has to focus on understanding it rather than being free to travel to all these weirdo places."
Elliot's catchphrase in the novel is "No interruptions". (It usually precedes a long, self-aggrandising anecdote.) Rich says this has always been his motto as a writer. "A great piece of advice that one writer gave me at college was 'Skip the boring parts'."
That's great, I say. But how do you know where the boring parts are? If writers knew when they were being boring and could act on this knowledge, the history of literature would look very different. There'd be no Tristram Shandy, no Piers Plowman.
"I think, in my case, it comes from being a graphomaniac, from just throwing so much stuff against the wall," says Rich. "I churn out a shocking number of horrible things, then I go back and hope that one or two will be salvageable. None of my work is particularly precious to me."
He's temperamentally well-suited to writing TV comedy, then.
"Yeah, it's perfect. And I come from a magazine world where you throw it all out there and wait for the rejection slips to come back. If even one scores, then you feel you've had a good week."
Now, this is where some critics raise their eyebrows. Rich is undoubtedly a comic wunderkind whose talent cup runneth over. But how many rejection slips has he actually received in his life? How many 26-year-olds whose fathers are not the veteran New York Times columnist and former "butcher of Broadway" Frank Rich get to contribute offbeat, elliptical "humour pieces" to The New Yorker? Not many. But then you can turn that around and ask how many 26-year-olds are writing offbeat, elliptical humour in the first place. Even fewer - and I'd guess none of them is as good as anything in Rich's two previous books, the collections Free-Range Chickens and Ant Farm.
Rich grew up on 15th Street and 1st Avenue in the middle of Manhattan. "I was a fearful kid," he recalls, "always convinced a murderer was going to escape from prison, climb up to our apartment and destroy us." At school, he was "a pretty typical nerd, constantly reading and writing, failing with girls, starting humour magazines for me and my friends that nobody would ever read".
At Harvard, he became the president of the university's satirical magazine, the Harvard Lampoon: "All my friends were doing noble things like learning how to be doctors and I was in a basement arguing about the merits of the Benny Hill Show and writing thousands of jokes a day."
Didn't he have to break off occasionally to do some work?
"Harvard was a pretty non-academic experience for me. The classes I took tended to be electives on subjects I was really interested in, like mediaeval culture, religion, primates and insanity throughout history. [Deadpan face] I think these things really inform my writing."
The film rights to Elliot Allagash have been bought by Jason Reitman (Up in the Air, Juno). Rich has just turned in the screenplay, "so we'll see if they like it". He had to change a lot, but didn't mind: "I wrote it a long time ago and the distance felt wide enough... not that it was as if I hadn't written it, but I didn't shed a tear at having to rip it apart." He smiles. "It was great to be able to spend time with Elliot again."