Sinn Féin vice-presidential candidate John O'Dowd translated Tandragee as 'ass to the wind' after the British Prime Minister blew in for a flying visit on Thursday.
Mr. Johnston paid an unannounced visit to Tayto Castle and crisp-factory in County Armagh as part of a whistle-stop campaign tour.
"The Irish for Tandragee [sic] is ‘ass to the wind’ which may or may not be a coincidental reference to Boris!" tweeted Mr. O'Dowd.
He meant to say that Tandragee is an anglicisation of the original Irish place-name, Tóin re Gaoith, meaning 'backside to the wind.'
SDLP leader Colum Eastwood, meanwhile, said: “This Tory government, sustained by the DUP, has been bad for people, businesses and communities in Northern Ireland. Now, rather than facing voters to explain the pain they have inflicted on people here, Boris Johnson is running around Tayto castle in the dark. It defies belief."