The tears and rant were about more than one race. An accumulation of Olympic disappointments poured forth that day - from not making the team in 2000, to not winning 2004 gold in either the 100 or 200 breaststroke despite setting world records in both during the U.S. Olympic trials, to not even qualifying for the 200 at the 2008 Games.
Hansen regrouped to win his second consecutive 4x100-meter medley relay gold in Beijing, then declared himself done with swim meets.
For more than two years, he was. Still living in Austin, Texas, where he swam for the University of Texas, he started working in promotions with a start-up sports-drink company. He competed in triathlons. He got married.
"For so long I stared at a black line on the bottom of a pool and really didn't get to experience anything outside of swimming," Hansen said. "At the end of the day, I wanted more. I think that's what fried me a little bit in '08, knowing that I put so much of the rest of my life on hold to chase this dream."
Now 30 and bolstered by a fresh perspective, the Haverford High School graduate is swimming again and headed to the London Games.
"He needed a break," said his wife, Martha, a former Texas teammate. "But I think deep down he knew that it wasn't over."
Though Hansen's London competition agenda mirrors his Beijing schedule - he will swim in the 100 breaststroke and the medley relay - his approach is different.
"Every Olympics that I've gotten on the plane afterwards and been flying back to the U.S., I've been disappointed," Hansen said. "I want to set the right goals for myself. I want to make sure that I do what I can, and I want to be a really important part of this team, in and out of the water, and kind of leave my mark on it all."
With four individual world titles, five world records, and the two Olympic relay golds, Hansen lacks only an individual Olympic gold on his swimming resume. But that hasn't been the driving force in his return.
"The goal on this whole comeback was to make the Olympic team," he said. But the prospect of finally standing alone on an Olympic podium's top step still holds allure.
"A lot of people, like Michael [Phelps], Ryan [Lochte], and Natalie [Coughlin], they take it for granted because they've done it so many times," he said. "For me, one time would be enough."
Hansen's winning time of 59.68 seconds in the U.S. trials was the fourth fastest in the world this year. His best time in the event is 59.13 seconds, set in 2006.
Still at the top is Hansen's longtime rival, Kosuke Kitajima of Japan, who swept the individual breaststroke golds in the 2004 and 2008 Olympics. Kitajima, who swam the 100 in 58.90 seconds in April, also is making a comeback.
"Right now, I consider myself the underdog to win this," Hansen said. "I've always loved that position. In 2004, when I broke the world records and went into the Olympics as the favorite, it was a lot harder for me."
Hansen's comeback began on a December 2010 training trip to Florida for the Haverford School. Sean invited Brendan and Martha to join him because he was planning to propose to his girlfriend during the trip, and he wanted them there.
Brendan also helped his brother with the training. Sean saw strength in his strokes and a glimmer in his eyes. By the end of the week, Brendan was talking about a return to swimming.
"He never asked me what I thought about him coming back," Sean said. "But I said to him, 'What else do you have to prove? You have the medals, you have world records, you have the accomplishments. You have all of it. It seems the only thing you have left is to be disappointed. So unless you change your attitude towards it, I don't want to see you go back.' "
Hansen returned to Austin and met with Texas coach Eddie Reese. In a sport that has had its share of comebacks, in which a 41-year-old Dara Torres won 50-meter freestyle silver at the 2008 Olympics, Reese knew that Hansen could succeed.
"The thing Brendan has on his side is that same thing Dara has always had on her side: He's never gotten out of shape," Reese said. "When he first started doing triathlons, he would train all three events every day, six days a week. Nobody in their right mind does that. It's just the way he is, the way he approaches things."
A conversation with Martha pushed Hansen to commit 100 percent to the comeback.
"She's always been very matter-of-fact and just said to me, 'Are you going to regret this when you're 40 years old and we've got kids running around and you didn't try for these Olympics?' " Hansen recalled.
Within months, Hansen won the 100 and 200 breaststroke races in the 2011 national championships. A year later, he won the 100 at trials for his third trip to the Olympics.
He displayed a happiness that his family had not seen for years.
"His reaction afterward was like an 8-year-old when they get the heat-winner ribbon at a summer-league meet," Martha said. "He had a huge smile on his face."
He came up short in the 200, finishing fourth, as he had at the 2008 trials. But the day after, he was spinning it positive, pointing out that it allows him to focus on sprinting in his 11th-hour Olympic preparations.
"He's just fallen in love with the sport again and realized that it's all what he wants now," his wife said. "It's not proving himself or trying to show that he can make a team or do this or do that. It's all just about, 'Hey, I'm 30 and I'm still here and I'm actually doing pretty well, so let's see what else I can do.' "