I have been trying to think if I’ve ever felt sorry for Boris Johnson. I’ve felt sorry for Donald Trump, and each time that knee-jerk sympathy has felt like a failure. I had a twinge of it this April when he joked to a bunch of reporters’ kids, “I like you much more than your parents,” – quite a funny line, for Trump – and everyone went off the deep end. It flared up again this week when he put Halloween candy on a kid’s head instead of in his candy bag: a weird effort to be whimsical, I imagine, that was roundly mocked. He deserves no sympathy, but there is something about a lighthearted gesture falling flat that triggers it in me. By contrast, when a stadium of baseball fans booed Trump in Washington on Sunday night, it seemed an entirely appropriate and satisfying gesture.

For Boris Johnson, the booing of the US president and the undiluted happiness it gave many of us is an omen of what he might expect during the general election. While Jeremy Corbyn remains the kind of ornery fringe politician for whom opposition is a badge of honour, Johnson, like Trump, clearly needs to be liked. When he’s crossed in the Commons, his genial persona evaporates. When, as happened during his walkabouts in September, members of the public harangued him, he looked petulant and baffled, before neatly pivoting to whip up the crowd against Corbyn. The strength of his need, combined with the jokey tone he deploys to service it, sets up his critics – however reasonable and fair-minded – to long for the kind of closure that only public humiliation can fulfil.

Donald Trump at the Washington Nationals v Houston Astros game in Washington DC Photograph: Rob Carr/Getty Images

This is an odd inversion of a principle with which I used to broadly agree, that no matter how much you despise a politician, everyone deserves to be treated with a measure of civility. I remember Tony Blair’s appearance on a Question Time, a million years ago, during which a woman in the audience was monstrously rude to him. It was ugly and awkward, and seemed performative in a way that didn’t get anyone anywhere and I remember thinking it could never happen in America.

Well, now it has, and it’s sublime. After the booing and the chanting, the president’s defenders made the ludicrous point that the crowd’s behaviour was “un-American”, as if the chants of “Lock him up!” were original and not a sardonic commentary on Trump’s own prior performances. One can imagine a similar scenario with Johnson. The way he has gone for cheap gags his entire career – Muslim women as “letter boxes”, which for scorn is on a par with Trump’s mockery of a disabled reporter – is indecent in a way that calls for indecency in response.

Some who studied the footage said that Trump cried, although I didn’t see that. He did, however, look shocked, jolted out of his giant delusions by a stadium full of sports fans wearing red hats – for the home team, not for the president – from whom he had surely been anticipating support. It wasn’t pure schadenfreude, although there was that. But watching Trump forced to confront his own unpopularity and absorb some of the ugliness he himself has created was, for a brief moment, like a revenge fantasy made real, one in which – Johnson, take note – making someone feel bad was the ultimate political gesture.

• Emma Brockes is a Guardian columnist