At 188cm, O'Brien is almost smack bang in the middle of his club's list in regards to his height.
This week, when the 24-year-old was given the enormous privilege of meeting His Holiness the Fourteenth Dalai Lama, he dwarfed the renowned Tibetan spiritual leader so much it prompted a small giggle from the visiting Buddhist monk.
His Holiness had just ended his first group press call as part of his 11-day Australian visit, which officially began in Melbourne on Thursday.
After delivering a stirring address where he spoke of things such as "inner doors", and the benefits of having it "open" (influencing compassion, happiness and communication) as opposed to "closed" (indicating self-centeredness and influencing loneliness and feelings of sadness), His Holiness was open to questions.
O'Brien, among the many interested listeners in attendance at the Hilton Hotel press opportunity, was one of the few keen to ask His Holiness for his thoughts on a topic close to his heart.
He asked how people of influence could help spread the message about embracing diversity and the importance of the interdependence nature of all things; an interest very significant to the half-Brazilian, half-African O'Brien.
His Holiness' response was centred around a natural changing of the guard.
"My century is gone. Now, I say 'bye bye'," he said.
"You, the younger generation, all the responsibility to make a better world, a peaceful world, a less fearful world…please you take full care for the rest of the century.
"My generation will either go to heaven or hell…and from there we will watch you."
Afterwards, O'Brien reflected on His Holiness' words and said they were an "affirmation for my life's purposes".
"Living in Melbourne, which is very diverse, I've dedicated a lot of my time to bringing people together from all walks of life, and hearing His Holiness's answer just reaffirmed to continue on that path," he said.
"It also told me to ensure that this generation, my generation, handles the future responsibly."
His Holiness said ensuring diversity was accepted fell to people like O'Brien, who he took an instant liking to the moment the Magpie stretched to his full height and approached his perch.
O'Brien took to the small stage where His Holiness' armchair sat once the formalities were over, and stood more than a full head over the Tibetan spiritual leader much to the amusement of the small-framed monk.
Still, the closeness between the two was evident. His Holiness made fun of their height difference, and then curiously rolled one of the premiership defender's dreadlocks in his fingers.
O'Brien, who presented His Holiness with a Sherrin football and Collingwood guernsey, became emotional when he received his own gift - a traditional white scarf known as a 'khata' - a symbol of purity - and a warm embrace.
"It's derived from love itself and those emotions are very overwhelming," O'Brien later said.
"I think it symbolises such an amazing day of my life.
"Not many people get an opportunity to meet His Holiness and for me to be invited to attend and be an official ambassador is an amazing thing.
"This gift from him also symbolises the message he gave today and also the affirmation that I have now for my life to continue on this path."
It wasn't just the answer to O'Brien's specific question that had the deep-thinking Magpie enthralled.
His Holiness' messages regarding inner strength maintaining inner peace, and how he visualises "hard line" Communists in China and directs compassion, tolerance and forgiveness towards them in a bid to help "calm his mind" really made an imprint on the defender.
"Everything that His Holiness speaks about is from the essence of love and compassion, and understanding the interdependence of all phenomenon, whether it be the relation the humans have with their nature or each other," O'Brien said.
"From that understanding, that's when you can act out of compassion for everything.
"I think all the answers he gave this afternoon were in relation to that; having that compassion in your heart to be able to make the world a better place and in turn, making the world a better place is actually making yourself a better individual - for your health and your mental state."
His Holiness was first asked about his feelings on Prime Minister Julia Gillard's decision not to schedule a meeting between the two during his visit to Australian shores.
He smiled, in his immensely likeable and infectious way, and said he wasn't concerned as he had no political agenda to push during his trip.
He was then asked about the current scandal involving Ricky Nixon and the infamous teenager, and what he thought about society's approach to drugs and what caused such issues to occur in the first place.
In reply, he spoke to a lack of "moral education" and how drug and alcohol abusers struggled to find inner peace on their own.
Nearly an hour later, it's fair to say everyone in the room felt a greater level of that inner peace he so regularly mentioned, influenced by the smiling, peaceful visitor who you couldn't help but feel connected to as he delivered the memorable line, "Everyone has the right to achieve a happy life".
