Chipotle Mexican Grill, Inc. (NYSE: CMG ) reported fourth-quarter earnings Tuesday afternoon, meeting expectations on revenue but far surpassing Wall Street's earnings expectations. Chipotle stock rose as much as 6 percent but quickly gave up most of those gains. In after-hours trading, shares wavered, trading down as much as 5 percent.

At the close of trading on Tuesday afternoon, CMG stock, once one of Wall Street's most impressive growth names, was down 25 percent in the last year and 3 percent in the last five years. The Standard & Poor's 500 index rose 17 percent and 78 percent over the past one and five years, respectively.

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That is some truly horrendous underperformance, and it's clear that the most recent Chipotle earnings report is one people may look to as the beginning of a new era for CMG stock. Wise investors will make that an era during which they don't buy the stock.

CMG earnings by the numbers. The Denver, Colorado-based burrito chain reported earnings per share (EPS) of $1.55, up 182 percent year-over-year. Revenue came in at $1.11 billion.

Analysts were expecting EPS of $1.32 on revenue of $1.11 billion in the fourth quarter. The earnings beat was impressive, no doubt.

There were a few other important metrics from Chipotle earnings: Same-store sales rose 0.9 percent, and restaurant level operating margin was 14.9 percent. Both of those numbers came in modestly below expectations: Analysts surveyed by FactSet were expecting comparable sales growth of 1 percent and an operating margin of 15.9 percent in the fourth quarter.

A glacial recovery, if you can call it that. Anybody paying even casual attention to Chipotle's situation is aware that the company's struggling to recover from a string of food safety crises that began in 2015. Hundreds of people, customers and employees alike have fallen ill due to Chipotle's food , coming down with E. coli, salmonella and norovirus.

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Unfortunately for shareholders, the food safety crisis has morphed from a temporary nightmare into a permanent blemish on the brand and its popularity. It's been less than seven months since the most recent crisis, a norovirus outbreak at a Virginia location that sickened more than 100 people.

CMG stock peaked around $750 per share in August 2015. It finished the session Tuesday at $304.33.

Chipotle shares: a bad risk-reward. Regardless how the market as a whole interprets this Q4 report, there's only one sensible takeaway: Don't buy.

Margins and same-store sales are still weak, and worse than expected. More importantly, Chipotle's brand remains tarnished, and that is proving extremely difficult to repair.

From a simple valuation standpoint, CMG stock also looks expensive. Shares go for more than 50 times earnings and about 30 times forward earnings. If you're an enterprise software firm, maybe that makes sense. But not a restaurant chain with image problems.

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Chipotle expects same-store sales growth in the low single digits in 2018 and expects it will open between 130 and 150 new locations. The new CEO search is still ongoing, though, and that likely has its own overhang on the stock. "Whatever they say right now is irrelevant," Wedbush analyst Nick Setyan said on CNBC about the conference call. Until a new CEO is picked, hearing plans from the outgoing chief is like talking to a lame duck Congress about future legislation.

At the end of the day, Chipotle just hasn't been incident-free long enough to regain customers' trust. Assuming it takes two consecutive years of no outbreaks for the public to largely regain trust in Chipotle, that day is nearly 18 months away. Even then, it won't be the phenomenon it was in 2015. And even if it were, there would still be latent doubts.

Let this dog lie, at least until he proves he can learn a few tricks.

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