Extinction Rebellion activists were positioned outside Burns The Bread in Glastonbury, Somerset, prompting a decision to divert the Prime Minister to one of the company's shops in Wells.
Signs held by the protesters included one reading "Greedy fat Tory clown" and another which had Mr Johnson's face with the word "Twat" written on it.
The PM's team opted to switch location and he did not arrive at the Adlam Central Park venue.
Instead, Mr Johnson received a warm welcome in Wells and he served sausage rolls and pasties to customers.
Reflecting on the change of plan, he said: "There were lots of crusties there - more crusty than your loaves."
The Prime Minister then went on a short walkabout in Wells High Street, where he was cheered and welcomed by several people although there was some heckling from a handful of others.
He also visited a card shop, where he was presented with a card featuring a bulldog with a mop of blond hair located in Downing Street.
But Lynnsey Kelly, who runs a flower shop in the city, said of the Mr Johnson's visit: "Right at this very moment in time are there not more important things to be done in this country than the Prime Minister coming to somewhere like Wells and serving pasties to people and having a photo opportunity?
"It is absolutely disgusting."
Around 100 protesters, including members of Extinction Rebellion, the Labour Party and anti-Brexit campaigners, had gathered outside the bakery in Glastonbury to await Mr Johnson's arrival.
One protester, who did not give his name, said of Mr Johnson's change of plans: "It doesn't surprise me if you look at the ten Tories that are here to welcome him compared to 150 people here.
"He knows there is a large proportion of the population that sees through him and understands the sort of man he is.
"He has got no clue what any of these people feel and what their daily experiences are like."