He had taken issue with a notion about him that has been floating around Hollywood the past few years. Namely, that the actor's ego is even more outsized and buffed up than his muscle-bound physique.
And that Diesel had turned his back on sequels to The Fast and the Furious - the cinematic thrill ride that made him a household name - out of some overly inflated sense of self.
"If somebody wanted to say my ego prevented the second one from being a real sequel, that's cool," said Diesel, wearing wrap-around sunglasses and a T-shirt that emphasised his grapefruit-sized biceps.
"I turned down US$25 ($NZ43 million) for my ego? If my ego is healthy enough to say, `I'm not going to do a ... rehash of the same film just because you want me to do it quickly'," - he slaps his palm with the back of his hand impatiently - "that's my ego! My ego is that big!"
In 2001, the chrome-domed actor cruised on to the A-list as the star of The Fast and the Furious, which followed a multicultural band of street racers (and the women who love them).
The movie surpassed all expectations, grossing $207 million worldwide.
But Diesel declined to return for 2 Fast 2 Furious (2003) and seemingly bailed on the franchise, except for an unpublicised cameo in 2006's The Fast and the Furious: Tokyo Drift.
The intervening films found some success at the box office, but no true sequel reuniting the original cast members (Jordana Brewster, Paul Walker and Michelle Rodriguez) has reached the screen until now, with Diesel headlining the fourth instalment, Fast & Furious.
Diesel had just appeared on The Tonight Show With Jay Leno, but the actor - who broke character type by working with director Sidney Lumet on 2006's modestly budgeted Find Me Guilty - was only getting started on the E-word.
"If someone defines my ego as being the last arbiter on quality on a script, then so be it," he said.
"My ego is so big that I'm going to say, `Whoa, kemosabe!' My ego is big enough that I'm going to say: `Not interested. I'd rather not have this wonderful opportunity. I'd rather not have the money and work for free with Sidney Lumet.' Because of my damn ego."
And yet here is Diesel (41), reprising his role of Dominic Toretto - a wheelman with a heavy right foot and antifreeze in his veins - whose motto in the first Fast film is: "I live my life one quarter mile at a time."
In Fast & Furious his character, now an international fugitive, returns to Los Angeles after being wronged by a ruthless drug cartel.
Abetted by the undercover cop (Walker) who nearly brought him down in The Fast and the Furious, Toretto infiltrates a cadre of drug-runners - who race the product in from Mexico in souped-up hot rods - in order to exact revenge on their kingpin.
The actor says his decision to pass on the second Fast film - not to mention turning down xXx2, the sequel to his 2002 hit xXx - was dictated by the quality of the material as well as a fear of getting stuck in a certain character type.
"I always get afraid of being pigeonholed," Diesel said. "Which is why it takes me so long to return to characters. Probably longer than most people would like.
"But the real reason why I didn't return to the characters is the scripts hadn't been right. The characters haven't been right. It's not like I ever said I wouldn't be there."
To wit: When the director of The Fast and the Furious: Tokyo Drift, Justin Lin, approached Diesel about making a cameo appearance, the actor ignored his representatives' advice.
"All my reps, including my agent, said, `Don't do it'," Diesel recalls. "They felt it could be me misleading the audience and was too risky."
Ultimately, however, that cameo brought him back into the fold.
It opened negotiations that led to Universal, the studio distributing Fast & Furious, making Diesel an offer he couldn't refuse.
"We started talking to him about developing a Dominic Toretto movie," said Neil Moritz, who produced all four The Fast and the Furious movies.
"We were calling it Toretto. It wasn't going to bring the whole cast back. But that was the jumping-off point for the new movie."
Toretto was eventually put on the back-burner in favour of reassembling the original cast.
Diesel exercised creative control in updating the characters' motivations - such as Walker's police detective character coming to terms with his conflicted code of honour amid skid-outs, gun blasts and car crashes - and "redefining their existence in weird ways."
And he shot a 20-minute prequel to Fast & Furious called Los Bandoleros that Diesel says will explain what the Fast characters have been doing since viewers last saw Toretto. (The short will be included in the movie's DVD release.)"It's Dom in the Dominican Republic.
How I reconnect with Michelle [Rodriguez's character]," he said. "There's no car chases, no car scenes.
"It's all character. Justin always calls it the `Anti-Fast'."
Lin recalls spending hours discussing half a page of dialogue with Diesel, whom he describes as "meticulous."
But the director also bonded with the actor, whose early experience as a director (Diesel's feature directorial debut Strays premiered at the 1997 Sundance Film Festival) caught the attention of Steven Spielberg and led to Diesel being cast in his breakthrough role as a World War 2 grunt in Saving Private Ryan.
"Vin doesn't make things easy," Lin said. "If I didn't come into the film with clear ideas of what I wanted to accomplish, there would have been big trouble."
Moritz said: "It's not about ego. Vin just wants what's best for the movie." - Chris Lee
