"Don't do drugs. Don't do stupid stuff," he said. "It's stupid to do it anyways, regardless if you're driving race cars or not. It's a dumb idea. Just don't be ignorant."
Nothing else really needs to be said. We have known for weeks that Mayfield was suspended, according to court documents, for taking an amphetamine that NASCAR attorney Paul Hendrick called a "dangerous, illegal, banned substance."
We got more specific Tuesday, calling the illegal substance methamphetamine.
It could have been crack cocaine or marijuana. It doesn't really matter.
It is illegal. There is no defense against that.
Unless Mayfield's attorneys can prove the test was tainted and that the driver hasn't taken drugs, his career is over. No major sponsor will touch a driver proved to have taken illegal drugs, and without sponsorship it's nearly impossible to get on the track.
That is why Mayfield has no choice but to challenge NASCAR. Going through the rehabilitation process mandated for readmittance basically is an admission of guilt.
With that stigma at the age of 40, unless Mayfield strikes oil on his North Carolina farm he'll never have the financial backing to put a competitive car -- or maybe any car -- on the track.
So he's fighting.
How this will turn out is up to the court. Mayfield's attorneys would like the entire test thrown out, arguing that the "B" sample was tested at the same laboratory as the "A" sample, and that goes against federal employee drug testing guidelines.
NASCAR will argue it is not a federal institution and that it was perfectly within its rights to test at the same laboratory. That the NFL and Olympic guidelines are the same can't hurt.
More importantly, they will argue that a driver with an illegal substance in his system shouldn't be allowed to compete.
So what have we really learned over the past 24 hours? Not much. Drivers are no more willing to rush to judgment now than they were a month ago. Most are waiting for the legal system to run its course before making bold statements.
Do they want to be on a track with somebody taking an illegal substance? No more than any of us want to drive down the interstate with somebody on drugs or alcohol. Did they suspect Mayfield was on drugs? No. And some aren't even sure it's fair to say he was until this is settled.
"Let me put it this way," Carl Edwards said Wednesday in a conference call. "I never have been racing people that are incapable of racing at this level. Most of the time I feel like I'm the idiot out there, like I'm in somebody's way or I have been screwing up.
"I always have looked up to these people in racing, Jeremy included. I never have gotten out of the car and said, 'Man, that guy is dangerous. Something is crazy here.' "
That NASCAR now has a legitimate system in place to catch somebody on drugs is the real story here. Under the old system of testing for reasonable suspicion, this likely would have slipped through the cracks.
Nobody suspected Mayfield was guilty of anything until he took a random drug test in Richmond that turned up positive.
And even that's not a guarantee in NASCAR or any sport. Suppose Mayfield hadn't been randomly selected?
"When you go in for surgery you don't know if the doctor cutting you open has some sort of personal problem," Edwards said. "That's life. All you can do is the best you can. I don't know what Jeremy did. I have no clue.
"Nobody would say it's all right to race on the track with somebody that is impaired. NASCAR is trying to do their best, and I feel good about it."
That being said, the federal judge who some time later this month will be asked to grant Mayfield a temporary restraining order allowing him back on the track until the case has been solved has no choice but to say no.
As long as there's any question a driver is guilty of taking an illegal drug, he shouldn't be allowed on the track.
"Either one of two things has happened," Edwards said. "Either he was into meth or he wasn't. If he was, then he's got a bigger problem than they think and we should try to help him out. If he didn't use any meth, we sure the hell should not be talking about it. It's certainly destructive to somebody's life and public image."
Or, as Earnhardt said, "Don't do stupid stuff."
That's all we really need to know.