He also wrote that Obama was wrong to move a statue of wartime Prime Minister Winston Churchill out of the Oval Office - and Churchill's grandson Nicholas Soames is not happy about it.
Soames has been a Conservative MP since 1983 and is a long time supporter of Britain's membership of the EU, so it's no surprise he didn't like Johnson's Euroscepticism. But, what Soames really disliked was Johnson's use of his grandfather to illustrate why Obama doesn't understand Britain.
Here's what Johnson wrote in the Sun on Friday morning, the added emphasis is ours.
Something mysterious happened when Barack Obama entered the Oval Office in 2009. Something vanished from that room, and no one could quite explain why. It was a bust of Winston Churchill - the great British war time leader... But on day one of the Obama administration it was returned, without ceremony, to the British embassy in Washington. No one was sure whether the President had himself been involved in the decision. Some said it was a snub to Britain. Some said it was a symbol of the part-Kenyan President's ancestral dislike of the British empire - of which Churchill had been such a fervent defender.
Johnson then basically said that Churchill would have supported a Brexit.
At the very heart of Winston Churchill's political beliefs was what he saw as the supreme right of every voter, with his or her little pencil, to decide who governs the country.
Soames started tweeting at Johnson using the hashtag #growupgetreal to voice his frustration.
Appalling article by @BorisJohnson in Sun totally wrong on almost everything. Inconceivable WSC wld not have welcomed Presidents views
- Nicholas Soames (@nsoamesmp) April 22, 2016
@BorisJohnson it is not compulsory to have head of WSC in President's office. Stupid irrelevant empty point to make #growupgetreal
- Nicholas Soames (@nsoamesmp) April 22, 2016
@jeremywils0n @BorisJohnson oh yes until he gets it right
- Nicholas Soames (@nsoamesmp) April 22, 2016
Soames wasn't the only politician to be offended by Jonhson's column. Labour MPs Diane Abbott and Chuka Umunna Tweeted that they were unhappy that Johnson used the words "part-Kenyan" to describe Obama.
Boris dismissing President Obama as "half-Kenyan" reflects the worst Tea Party rhetoric #offensive https://t.co/fbFZilJ0Wf
- Diane Abbott MP (@HackneyAbbott) April 22, 2016
These Tory Mayoral types are beyond the pale.Zac plays on @SadiqKhan's Muslim heritage, while Boris plays on @BarackObama's Kenyan ancestry
- Chuka Umunna (@ChukaUmunna) April 22, 2016