He's not going to win, regardless of the topic, regardless of how much he knows -- or thinks he knows. Politics. Current events. Helmets. Concussions. Even the NFL, in which Glennon has played five more years than Rosen, a rookie drafted in the first round in April.
It doesn't matter.
Rosen's an information forager. He's an avid reader and listener of podcasts. Once he finds something -- anything -- that interests him, he tends to dive into an information rabbit hole.
"I don't know enough to win against him," Glennon said. "I mean, he loves to debate. I don't even know if sometimes he feels that way, he just wants to debate it.
"He's very passionate about what he believes in. If you're going to debate him, you better have your facts ready because he's got his ammo ready to go with whatever you counter with him."
But when it comes to football and Rosen's job as the starting quarterback of the Arizona Cardinals, Glennon has noticed that Rosen doesn't argue just for the sake of arguing.
He switches tactics.
"I will not run a play on a football field unless I know why we're running it and what we're trying to accomplish." Josh Rosen
He still wants to know as much, if not more, about football than he does about anything else. But Rosen, an economics major at UCLA, does it by asking his favorite question.
"I will not run a play on a football field unless I know why we're running it and what we're trying to accomplish," Rosen said. "That's just how I function. I don't run a 4.5 [second 40-yard dash], so if things go bad, I can't just hit the exit button. So, I like to understand a playbook in its entirety."
Tight end Jermaine Gresham has seen plenty of quarterbacks throughout his nine seasons and says many of them want to know only what they're doing. Rosen, who's 21, wants to know what everybody on the field is doing, why they're doing it and how it fits into the big-picture of what the Cardinals are trying to accomplish.
In other words, he wants to know everything.
And he figures it out by asking, "Why?"
"He doesn't leave anything to chance," wide receiver Larry Fitzgerald said. "'Hey, this signal looks a little different than this signal. Let's talk about this. If we get this look, I want you to be thinking this. Just push your depth on this one because I'm going to be working the front side.' He's very meticulous in his details and that's going to serve him well in the future."
Fitzgerald, who's in his 15th season, is a strong believer in asking questions to learn. Mistakes, Fitzgerald said, can be avoided by asking that simple question.
Shortly after he was drafted in April, Rosen texted Fitzgerald about a little bit of everything: football, life, finances, to name a few.
Rosen's teammates might describe him as "different," as Fitzgerald did because of Rosen's seemingly never-ending inquisitiveness.
"He definitely thinks differently than any 21-year-old I know," Glennon said. "Let alone, probably, I'm 28, I don't know anyone that thinks like that.
"He's extremely intelligent."
Most of his teammates and coaches have never seen a quarterback ask so many questions.
"I think he's just a curious person who wants to know the answer to everything," said Charles Kanoff, the Cardinals' practice squad quarterback who's become one of Rosen's debate partners. "He doesn't take 'Because this is the way it's always been' [as an answer]. I think he's very against that idea and he always wants to probe deeper."
Coach Steve Wilks saw Rosen's curiosity and inquisitiveness from the first practice during rookie minicamp in May.
Wilks wants his players to ask "Why?" He also wants his coaching staff to teach the "Why?"
And no one gets the brunt of Rosen's questions like Byron Leftwich.
Leftwich started the season as Rosen's quarterback coach but was promoted to interim offensive coordinator on Oct. 19. And even though Leftwich encourages Rosen to ask anything and everything, it's been an adjustment for the 38-year-old coach, who worked with quarterbacks around his age the last two seasons in Carson Palmer and Drew Stanton.
Now Leftwich is coaching someone who's younger than his 23-year-old niece.
"This kid is really 21 going on, like, 36," Leftwich said. "You guys talk to him. This is a smart kid. This is a well-informed individual. He loves the game of football. You love just talking to the kid. I love his perspective. I never let him hold back. I want to know everything he says. I tell him, 'There's no dumb questions' -- even when I don't understand the question.
"There's no dumb questions, though."
Leftwich makes it a point to find the answer to Rosen's questions if he doesn't have it, which has happened, Kanoff said.
Being prepared for a quarterbacks meeting has become a necessity with Rosen, not an option.
"You got to be prepared when you walk into that meeting," Glennon said. "Because if you don't dot your I's and cross your T's, you're going to be called out on it."
Leftwich has been patient with Rosen's questions because he understands it's all part of Rosen's development as a quarterback. Since Leftwich has taken over as offensive coordinator, his goal for Rosen has been to get him ready to have a long career.
Filling Rosen's head with the right answers is the way Leftwich believes that gets done.
"With this kid, I want to make sure we do it the right way," Leftwich said. "Take from the ground floor, ground level, and let's install everything we need to install in this kid for the long haul."
But if there's one person who can answer Rosen's questions, it's Leftwich, a former quarterback taken in the top half of the first round before playing nine NFL seasons.
"I know exactly what he's going through," Leftwich said. "I mean, exactly. It's almost identical. It's amazing. When he got his first start, I remember telling him I got my first start in my fourth game. The pattern has almost been exactly as it was for me."
And Glennon's been in the league long enough to understand the benefits of knowing the "why" to everything.
"It's better to want to know why because you get a better understanding for why the play is in this week, what are we trying to accomplish on this given play, why does a defense do this, how does our protections fit in to what they're doing, all those things," Glennon said. "Now, there is a fine line. Sometimes, you just got to go do it. That's the one thing. It's great to ask questions, but sometimes that's just the way it is. Sometimes that doesn't sit well."
Rosen doesn't reach that point often, Glennon said.
But, Glennon has noticed that Rosen responds well to coaching, even if all his questions aren't -- or can't be -- answered.
Yet, there have been times when Rosen starts asking too many questions.
"He's doing it out of wanting to be the best player he can be and help our team win," Glennon said. "Sometimes he does argue to argue. Not really when it comes to football. That's other stuff. He's usually doing it out of the best interest of the team and himself."