"I would tell people, for anybody who asked, although it rarely came up, that I was a ceremonial guard," he says. "And I loved that title because it doesn't mean a thing ... but it sounds official."
This marked the beginning of a long crashing career. He's also celebrated with Super Bowl and World Series winners.
"In my opinion, the Kentucky Derby overshadows every one of them. I don't think there's a better sports spectacle on the face of the Earth," Johnstone says.
His inspiration was a New York taxicab driver named Stan Berman. In 1961, Berman sneaked into the Academy Awards. He presented a homemade Oscar to Bob Hope on live TV for his movie The Big Broadcast of 1938.
"They made occasion of interviewing [Berman] after that experience, and the question came up, 'What's your next gig? Where are you going to be?' And his response was, 'Look for me in the winner's circle at the Kentucky Derby,' " Johnstone says.
To Johnstone's knowledge, Berman never made it there. But Johnstone has — 18 times — and he has pictures and dried roses to prove it. He's also never been caught.
He points to the door and hallway he has navigated to get onto the track after past races.
Stephen Johnstone and his friend, Sharron Reynolds, snuck into Derby celebrations in 1968. Reynolds is just behind the woman with the trophy; Johnstone is to Reynolds' right.
Courtesy of Sharron Reynolds
Courtesy of Sharron Reynolds
"We have gone through that, and walking hurriedly because the race is over and everybody is rather excited, and then just make our way onto the track," he says. "And then it's a case of associating with people who do belong there or who are interviewing various people and things like that."
Johnstone says, at that point, your job is to share the joy of the moment. He's done that many times, always with an accomplice. In 1968, it was his friend Sharron Reynolds. Johnstone told her to act as though she was the daughter of the person who had just won the Kentucky Derby.
"And so I was like, 'Daddy won, Daddy won! Daddy won this is so exciting! I'm so happy for him!' " Reynolds says. "And they took us right up and even pushed the governor out of the way so we could get up front."
Despite never being stopped, there have been close calls. Johnstone's niece, Sarah Johnstone, says in 2006 she made it onto the presentation stand and almost got caught.
"It was that moment when Bob Costas was asking, 'And your name is? And your name is?' ... and I was like, 'Oh my gosh, who do I say that I am?' You know, you can't say you're the trainer's niece when I could be standing right next to the trainer and his wife and not know it," she says.
Fortunately, Costas stopped asking the questions before his broadcast began.
Last year, Stephen Johnstone crashed the Kentucky Derby party following the race by pretending to be a reporter.
He says it was his final time, but he's still wearing that playful smile that shows up in historical Derby pictures.
"But then I remembered that the horse's name was I'll Have Another, so there's already a temptation there, I guess," he says.
So while Johnstone says he's done gate-crashing, his niece is making no promises.