The foreign secretary is reported to have used the swear word at a diplomatic gathering last week.
Asked about this in the Commons, he said he may have "expressed scepticism about some of the views of those who profess to speak up for business".
Theresa May said it was right the government listened to business voices about the terms of the UK's exit.
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Airbus, BMW and Siemens have warned about the impact on their UK-based operations if the UK leaves the EU next March without any agreement.
Their warnings have prompted different responses from ministers.
Business Secretary Greg Clark has said their concerns must be heeded but Health Secretary Jeremy Hunt said a warning from Airbus that it could cease operations entirely in the UK, threatening thousands of jobs, was "completely inappropriate".
Mr Johnson, who was reportedly speaking at the time to Rudolf Huygelen, Belgium's ambassador to the EU, was also overheard saying he and others would fight Theresa May's soft Brexit "and win".
https://www.bbc.com/news/uk-politics-44618154
