Charismatic Mr Johnson, who is widely seen as key to the Brexit camp’s chances of success on June 23, is touring the UK with his Vote Leave battle bus.
After their confrontation Mr Grigg, who is a student, said he had taken three eggs with him and put one in the pocket of a Vote Leave supporter.
Asked if he was going to throw them, he said: “No, I was not going to throw an egg. The egg was just to mess with them.
“The egg was to cause a scene.”
He added: “Today was a protest against the Conservative Party, it wasn’t to do with Vote Leave or the EU.”