It was the teenage star's second date at the venue this week as part of his Believe world tour, which lasts for almost a year.
But hours before the show began, teenagers showed FM104 a pizza box that Justin Bieber had 'given' fans after ordering fast food for his crew.
"He's just so amazing in every way. He's such a nice person. He does so much for his fans," explained Zara 'Bieber'.
"If we even think it's from him or he touched it or anything we've to touch it. We love it."
Justin Bieber's fans - nicknamed Beliebers - are infamous for being obsessed with the Canadian pop star and they're prolific on social media networks, where his career began.
Bieber fever has been compared with Beatlemania, but his fans have also shown a nasty side, issuing death threats to women he's reputedly involved with.
Zara revealed that her obsession with seeing the 18-year-old singer up close is the most important thing in her life.
"I've to be at the front, I love him so much. I've worshipped him for four years," she said.
Justin Bieber is much more important than school. I'm in love with him.
Fan Aoife didn't expect the FM104 presenters to appreciate why she was standing outside in the freezing cold.
"You've to be a Belieber to understand. It's like a religion - Bieberism," she added.
When 15-year-old Sharon 'Bieber' revealed she's planning to get Bieber's face permanently etched on her body, listeners were horrified. One even texted in to the show to tell Sharon they felt the same way about Brian McFadden.
"I'm getting a tattoo of him. I will be a Belieber forever," she declared.
"I pray to him every single night. I've a Justin Bieber prayer. I pray to God that my Justin Bieber dreams will come true. [They are] to marry him and get meet and greets. He's the most important person in my life."
Sharon travelled all the way to Dublin from her home in Cork and admitted she had got in a bit of trouble with her parents for taking off on her adventure. But she wasn't going to let a little thing like obedience stand in the way of seeing the singing sensation.
"I said I was doing it for Justin, I don't care what you think," she said.