The bulletproof diet is a modified version of the "Paleo" diet created by web-marketer and blogger Dave Asprey. Think about a "eat just like our caricatured idea of how malnourished cavemen ate" along with a "don't count calories" philosophy with suggested eating portions thrown in because, why the hell not?
Often the journals used by Asprey to justify his claims are heavily misinterpreted (for example, unequivocally recommending those following the Bulletproof diet eat white rice over brown rice because, beriberi be damned, according to one study white rice is a whole ~2% better at nutrient absorption). In some cases, the recommendations are outright rubbish, e.g. opposition to the consumption of sucralose and the recommendation of raw milk consumption.
Asprey's The Bulletproof Diet book (published in 2014) was negatively reviewed by medical experts:
Although the book tends to cite references accurately, it fared poorly in scientific accuracy due to dietary recommendations that are not well supported by the bulk of the scientific literature. It does not present convincing evidence that fungal toxins impact cognitive performance, and this seems unlikely due to the extremely small amounts found in typical foods and beverages.
The diet's unique selling point is that it promotes massive consumption of stimulants, specifically caffeine and US Schedule IV prescription drug Modafinil.  The Bulletproof Exec website recommends that breakfast be replaced by a large amount of 'Bulletproof Upgraded Coffee', a product sold by Asprey, mixed with a tablespoon of butter and a spoonful of 'Bulletproof Upgraded MCT Oil', a coconut oil derivative also exclusively sold by Asprey's company which he claims will deliver 'fast energy' to buyers.
The diet's website goes on to claim to its followers that the majority of people are "Suffering from a Modafinil Deficiency". This is complete and
udder utter bullshit since Modanifil is a synthetic drug. Asprey claims to having been on a 300mg daily dose of the stimulant for the past 9 years (together with use of synthetic hormones — 'testosterone replacement therapy.')
Hucksters all over the world make a lot of money selling exclusive products that they absolutely guarantee are essential. It's likely he makes a killing on selling caffeine hyper-doses and oil that serves no purpose except lining his pockets with your cash.