"Sorry thought I hit photo of Boris and Nigel, IM (sic) A TWIT", she later tweeted apologising to the former Australian prime minister.
US Democrat candidate Hillary Clinton was also the target of Johnson's column for "The Telegraph" in 2007 in which ridiculed the US Secretary of State's appearance.
Earlier this year, Johnson penned a five-line poem about Turkish president Erdogan, calling him a "wankerer", which won first place in The Spectator's President Erdogan Offensive Poetry competition.
Boris Johnson said he was "very humbled" to be appointed foreign secretary, and praised PM May for making a "wonderful speech", saying there was a "massive opportunity in this country to make a great success of our new relationship with Europe and with the world".
In another seemingly political disaster, Johnson then announced he supported May's challenger to become the next prime minister, not the home secretary herself.
Instead of choosing a team player, May chose a politician who prides himself on being different. To be honest, I find this outrageous but it's not just bitter for Great Britain. "It is vital that negotiations for Britain's withdrawal from the European Union, in particular, reflect the broadest political agenda".
In neighboring France, social media users expressed their surprise online. Boris Johnson has the delicate job of handling diplomacy; except, well, his previous interactions have been rather un-delicate.
And Mr Flynn said: "He has been sacked twice from previous jobs for not telling the truth. Shakespearean comedy or tragedy?"
Mark Toner, the spokesman for the US State Department, appeared to stifle a laugh when he heard Mr Johnson had been made foreign secretary.
He said: "We've today had warm words from our new prime minister about the need to stand up for more than a 'privileged few".
"This and it is an absolutely critical moment in certainly England's history, but also in the US-UK relationship so absolutely we're committed to working productively going forward".
Johnson's appointment has come as a surprise to many.
Online, however, the Chinese were more interested in Johnson's ample head of hair.
"Boris Johnson spent part of his life in Brussels; it's time for him to come back to Brussels, in order to check if everything he's telling the British people is in line with reality", European Commission President Jean-Claude Juncker said Thursday at the Group of Seven summit in central Japan.
She then entered Number 10 and began a reshuffle which started with Osborne being told he would not be a part of the new government and was being replaced by former Secretary of State Philip Hammond.