And yes, he was serious.
Gundy and his mullet starred in a campaign organized by the school's athletic marketing and social media departments, landing him a four-minute SportsCenter interview with mullet-wearing NHL commentator Barry Melrose in February on ESPN.
"I'm going to say that the dollar figure is somewhere in the millions for the amount of time that we've had on the air for that," Gundy said Tuesday during his news conference at Big 12 media days.
Asked to clarify later, the 49-year-old coach said the Cowboys, often overshadowed in their conference by heavyweights Oklahoma and Texas, gladly accept the publicity.
"We need to get our brand out there at Oklahoma State," Gundy said. "If you look back it, you say, 'What did you get out of it?' Well, OK, all of that happened at a time when nobody was talking about Oklahoma State football. Nobody was talking about college football, but our brand was out there all across the country."
Gundy credited the Oklahoma State employees for their ideas on how to promote him and his hair, which he recently trimmed.
"I get credit for it, because I'm the fool that stands up there and does it," Gundy said. "But they're the ones that think of it."
On the decision to trim his hair, Gundy said it grew long enough this summer for him to tie the mullet into a ponytail. He wanted to cut it, but his three sons preferred to see it grow. So he tied his hair back while at home and stepped outside, wearing a swimsuit.
Finally, after he had grown the mullet for a year, Gundy's wife, Kristen, stepped in to offer her advice: Clean it up.
Gundy also praised his hairdresser, who owns space at Klip It Up salon in Stillwater, Oklahoma, according to the coach.
"She's under a lot of pressure to make sure that it looks good," Gundy said.
After all, the hair is a source of marketing revenue for Oklahoma State.
"It's out there and people are having fun with it," he said, "so I guess we go with it."