During an interview with Arizona talk radio host Mike Broomhead, McCain was asked about Manziel, who gave the middle finger to the Washington Redskins' bench during a preseason game earlier this week.
"I just think he's gotta grow up," McCain said of Manziel. When you and I were his age — when I was a young Navy pilot, I'm glad that I wasn't on national television. That's all I can tell you."
McCain did offer some kind words for Manziel, calling the rookie quarterback a "great competitor."
The senator's rowdy youth is well-documented. A lengthy Washington Post profile published in 2008, when McCain was the Republican presidential nominee, focused on his unruly time at the U.S. Naval Academy, detailing a fight during his junior year at the school.
While on liberty, he and a couple of classmates had gotten into an argument at a Washington park with a group of guys from nearby Georgetown University who'd tried crashing an impromptu party that McCain and his friends were having with a few girls. An exchange of insults escalated to pugnacious challenges, then shoves, with McCain in the center of the confrontation. One participant remembers the dispute as bloodless, a simple case of testosterone briefly running amok among rival alpha males.
Whenever McCain sits down with Broomhead, it's a safe bet that the two will talk sports. In January, McCain used an appearance on Broomhead's show to call Seattle Seahawks star cornerback Richard Sherman a "loudmouth."
Listen to the interview below. McCain's comments about Manziel come at about the 1:35 mark: