'I didn't know anyone else cared about Linux commands'
He credits the Sandwich comic as the first to make him think he could seriously run a business based on drawing stick-men.
"I didn't know anyone else cared about Linux commands," he jokes. "After I posted that, my readership doubled overnight and I sold a whole bunch of shirts. Then there was one day where I was making more money than my day job."
Global fame then followed, with Munroe quickly crowned the king of geeks, his comic strips speaking to a new generation of people who (stereotypically, at least) find it easier to crunch hideously complicated equations than talk to the opposite sex.
Since then, so-called nerd culture has exploded into the mainstream via such offerings as The Big Bang Theory and The IT Crowd.
Munroe thinks there's "a little bit of a problem" about people who bond together over their love of technology or science, because by forming a tight little group, they deter others from joining in.
"People have found a label to put themselves under, but this can sometimes become self limiting," he says.
"There is a danger of building an identity around the idea of being smart because it is very easy to become off-putting, to become exclusionary. I try not to think about celebrating geek identity or appealing to smart people. That's not a healthy way to look at it."
As an example Munroe explains that when young he was rabidly anti-sports, defining his identity in sharp contrast to the muscled chaps who ruled the school corridors.
"I bought into the idea of jocks versus nerds for a long time, as I was insecure and prematurely defensive about not being into sport. But at some point you meet people who are excited about it and realise you are cutting yourself off from them.
"Take someone like Nate Silver. When he writes about baseball, I can see why he watches it. So maybe I can watch too. It's good to talk about science and be enthusiastic, without trying to build clubs."
Of course, this message can be lost on the hordes of fans who follow Munroe's every move. It was the fans who inspired his latest book, in which he answers their bizarre questions in depth.
His favourite questions is a doozy about what would happen if a boffin built a wall made up of all the elements in the periodic table. A quick clue: you wouldn't want to be on earth at the time.
In another, a fan asked what you would see if you stood in Times Square at various points over the past few million years. To find out, Munroe consulted a whole array of sources, studying the movement of glaciers to get a truly accurate answer.
However, although he's great when it comes to hard science, the webcomic author finds the fuzzy studies more difficult to tackle.
"People write in with very political or social questions, asking what would happen if we enacted so and so's policies," he says. "I feel as if they expect I can find a physics equation to answer this.
"Other people ask me what I can do to make someone love them again. And I sort of feel they need a hug, rather than an answer. Any social question is more complicated than a mathematical question."
Which he proves when I ask him about his homelife. Rather than answer in any detail, he just flashes one ring-clad finger to show he's married and declines to go any further.
It's not the sort of answer you'd expect from someone who lives in the eye of the internet, but then again Randall Munroe isn't your typical web celeb. He's the anti-Kardashian, the dark energy we all know is out there, but can't quite see properly.
Like the Higgs Boson he's got a mass, for sure, but we might just have to think of new ways to measure it. It's fame, but not as we know it. ®