Elon Musk's public persona is somewhere between a technocrat Willy Wonka and Doc Brown at 5am in the smoking area at Fabric - and he's just slipped closer to the latter than ever before.

One Twitter user suggested that by 2022 Tesla would be making something like the flying Delorean from Back To The Future 2, and Musk strolled into the thread to casually mention that that's exactly what he wants Tesla to do.

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The new Roadster will actually do something like this https://t.co/fIsTAYa4x8 — Elon Musk (@elonmusk) January 9, 2019

Given that Tesla's 2016 April Fool's joke was about a forthcoming flying car, many on Twitter wondered if Musk was joking. Musk was apparently not joking.

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I’m not. Will use SpaceX cold gas thruster system with ultra high pressure air in a composite over-wrapped pressure vessel in place of the 2 rear seats. — Elon Musk (@elonmusk) January 9, 2019

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Plus, you can basically accelerate at the limit of human endurance — Elon Musk (@elonmusk) January 9, 2019

Then again, this isn't the first time that Musk's restless brain has parped out an idea for a product that has then ended up either on the scrapheap or dissipated into the air before it got to the drawing board. Here are five of the best.

That mini-submarine, obviously

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Just returned from Cave 3. Mini-sub is ready if needed. It is made of rocket parts & named Wild Boar after kids’ soccer team. Leaving here in case it may be useful in the future. Thailand is so beautiful. pic.twitter.com/EHNh8ydaTT — Elon Musk (@elonmusk) July 9, 2018

The Thai football team trapped in a cave last year needed a hero, and they got several in the team of divers who risked their lives swimming to rescue them. They also got Musk running along behind them with what looked like a remote-controlled submersible coffin. It did at least exist, even if it was dismissed as "not practical for this mission" by Narongsak Osatanakorn, the head of the rescue mission's joint command centre, and told it "had absolutely no chance of working" by diver Vernon Unsworth. Then came all the "pedo guy" unpleasantness, the goading about how diver Unsworth should sue him if he really wasn't a "pedo guy", and the ensuing defamation lawsuit filed by Unsworth.

A website rating journalists' integrity

After becoming irritated by reports questioning the safety record of his Tesla factories, Musk suggested it might be a good idea to get the notably trustworthy and sincere people of the internet to rate and slate the trustworthiness of journalists and their outlets. A Ukraine-based news organisation had already taken pravda.com, but that didn't stop Musk.

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Problem solved, was able to buy https://t.co/ivSUwPqsDT! Game on … — Elon Musk (@elonmusk) May 25, 2018

Nothing much has happened with Pravduh as yet, but rest assured that 4Chan and Reddit will treat it with the respect it deserves if it ever materialises.

An electric pick-up truck

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I promise that we will make a pickup truck right after Model Y. Have had the core design/engineering elements in my mind for almost 5 years. Am dying to build it. — Elon Musk (@elonmusk) December 26, 2017

This is still at the prototype stage, but whether it'll ever see the light of day/the showroom is up in the air. Musk has said on Twitter that the pick-up truck was due for a big push on 2018, but it's still yet to surface.

One of the world's first online banks

Musk founded X.com in November 1999, intending for it to be at the vanguard of a wave of internet-based banks. He left in 2000, though, after which X.com ended up merging with another bank and being renamed PayPal. In a later plot twist, Musk then bought back the rights to the X.com domain in 2017. It was used to advertise a hat sale on The Boring Company website, which as a pay-off for nearly 20 years of mythos isn't particularly satisfying.

A cyborg dragon

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Oh btw I’m building a cyborg dragon — Elon Musk (@elonmusk) April 25, 2018

To be fair, he might have meant the SpaceX Dragon cargo spacecraft designed to drop off supplies at the International Space Station, and which has just completed its first successful mission, but it's not a proper dragon.

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