Born in the USA
In order to meet the eligibility criteria to stand for the presidency of the USA you have to be born in the country, have citizenship, be aged over 35 and have had residency for fourteen years. Boris Johnson meets the first three criteria.
I wouldn't wish Johnson on my worst enemy but I make an exception when it comes to the US so if he 'does a Harry' and flounces off Stateside in a strop he could in theory, after ten years, run in a presidential race. Of course, he'd have to gain the Republican party nomination first but, post-Trump, that might be the easiest bit. Johnson was born in the Upper East Side of Manhattan, New York City, in 1964 and spent his early years living in Washington DC before his parents returned permanently to the UK in 1969. In later life he announced that he would renounce his US citizenship (either a ploy to elude the US tax system or an election 'promise' - possibly both) but, true to form, it seems he never actually got round to it.
As things have turned out he's probably glad he didn't. He seems to spend an inordinate amount of time over the pond these days (certainly more than he ever did in Uxbridge and South Ruislip), chasing the 'Yankee Dollar' as a guest speaker on the American after-dinner circuit, so he might as well make the move out there. He won't be missed, that's for sure. One Tory ex-minister, Tim Loughton, has already told him to "shut up and go away" (at least I think he said go away).
In such circumstances it's always wise to keep your options open.