To know Mike O'Brien is to know that he is a huge fan -- and defender -- of all things Boston sports.
He also narrates for Boston Duck Tours, which is exactly what he was doing when he happened to see Golden State Warriors head coach Steve Kerr on one of the city's streets.
Kerr is, of course, in the city for Games 3 and 4 of the NBA Finals.
O'Brien tells NBC10 Boston the duck boat was struck in traffic in the Back Bay earlier this week with a full boat of tourists when he spotted Kerr.
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"When you are heckling a world champion NBA coach, you are not really thinking," O'Brien said. "Immediately just flipped a switch and I just started going on, 'do you know what we do in these duck boats?'"
"It was a lot of fun and it was just one of those, I can't believe this is happening type things," he added.
And O'Brien says Kerr dished it back.
"He said something about how we haven't done anything since the 80s, which is statistically incorrect because we have done everything in duck boats including the Celtics win in 2008," O'Brien said.
Of course, duck boats are the ride of champions here in Boston, including back in '08 -- the last time the Celtics won it all.
O'Brien is ready for history to repeat itself and for the Celtics to get banner No. 18.
"Let's cue the duck boats!!" he said. "There is no jinxing, the Celtics are going to win, there is no other reason why, we are doing a parade and I hope to be in that parade in some capacity."