Big online marketing mistakes seem all the rage these days. In late August, Spanish clothing and accessories retailer Zara got into hot water over what appeared to be a yellow Jewish star on a kid's striped pajama top that looked like prison gear. Then there was Urban Outfitters with the Kent State sweatshirt that sported what looked like bullet holes and blood stains.

When confronted with evidence of what angered people, at least they managed to cleanly remove the offending items. It doesn't make things all better, but it's an important first step. If only Walmart had learned that lesson.

The company has just gone through a one-day rollercoaster with marketing stomachs likely still heaving. It all started with Walmart's Halloween costume. Someone noticed a different subsection on the company's website: Fat Girl Costumes, as the blog Jezebel reported.

And that started the very-bad-not-so-good day for Walmart's marketing department. Even as the story was hitting online media and complaints were landing in the company's social networking accounts--the term "fat girl costumes" apparently hit the top 10 of Twitter trends--things moved slowed at Walmart. Jezebel noted that by 11:15 a.m. eastern, there was still a fat girl costumes section, although there were no items in it.

Well, at least things couldn't get worse, could they? Uh, actually, yes, they could. I had been asked by another editor to cover the story (not the marketing and business implications) the same afternoon. And when I looked, the fat girl costumes section was replaced by "Women's Plus Size Halloween Costumes." However, at the top of the page was a new banner that read: "Make it a monstrously big Halloween for less."

Really, did no one have a lick of common sense? A phrase like that on a plus-size targeted site would be bad enough. After the nonsense earlier in the day, it is an outrageously dumb oversight that, as of 4:30 p.m. on Monday, was still visible.

Walmart apologized for the slight, according to Bloomberg Businessweek. "This never should have been on our site in the first place," a spokesperson told them. "It's unacceptable that it appeared, and we apologize."

But an apology that has such an unfortunate fix is emptier than no apology at all. Here's a simple rule for when your company plants its collective foot deep into the muck: Find out what happened and make sure you follow up and actually look at the fix. Don't just trust whatever someone happens to tell you. See what your customers see. Your reputation is on the line, and it's too easy to slip from bad to worse.