So McDonald’s (MCD) should have known better when it got knocked on its heels after launching a Twitter campaign on January 24. The idea wasn’t a bad one — pay for a couple of promoted tweets encouraging customers to get in touch with farmers. First, the company pushed the hashtag #meetthefarmers. But in the middle of the campaign, the fast-food goliath introduced the hashtag #McDStories, hoping to stir up good press about consumers’ experience at its restaurants.

The first hashtag was saying, “Here are the great people who make our potatoes.” The second says, “Tell us what you think of us,” which, in the Web world, is risky business.

McDonald’s found that out the hard way. The promoted tweets received 72,000 responses, McDonald’s head of social media Rick Wion tweeted, and only 2% were negative. But many of the tweets were just plain mean, gross or, even worse for McDonald’s, hilarious. There was enough of a negative response that McDonald’s, which did not respond with a comment for this story, pulled the campaign a couple of hours post launch.

Granted, this is not a major corporate crisis, says Sharon Napier, CEO of Rochester ad agency Partners + Napier. “It didn’t kill people or change our environment. McDonald’s just made a really silly promotional mistake.” But the company should have never let this happen in the first place, she says, and mistakes such as these aren’t harmless.

Bad press can hurt a brand, even when comments are meant as a joke, and even if they are over-the-top, says Gavan Fitzsimons, a professor of marketing and psychology at Duke University. “Once you have a negative association, it’s almost impossible to just remove the link from people’s minds,” Fitzsimons says.

Companies would be wise to know that before they stumble into a social media fiasco. “As much as everyone believes that the mobile world is this wonderful petri dish, companies should never feel caught by surprise when news turns negative,” says Andrew Pierce, U.S. President of brand consultancy firm Prophet.

Staying prepared for negative press requires knowing the medium — consider social media success stories. Procter & Gamble (PG) released a marketing campaign in June 2011 with actor Isaiah Mustafa dishing out pithy responses via YouTube to tweets. According to P&G, 2,000 people sent in questions and the company posted almost 200 videos in response. The advertising stunt boosted P&G’s Old Spice sales and attracted tons of followers on Facebook and Twitter, P&G claims. The campaign tapped into something that generally gets great play on Twitter: irreverent, funny content.

That’s the type of content that hijacked McDonald’s campaign too. Case in point: @SkipSullivan, who describes himself as “pretty awesome at most things in life” on his Twitter profile, tweeted, “One time I walked into McDonalds and I could smell Type 2 diabetes floating in the air and I threw up. #McDStories.” It’s sick, it’s impossible, but people thought it was funny. And McDonald’s, which is performing well financially, doesn’t want people to see its name and diabetes in the same sentence.

A critical difference between the two companies’ campaigns is that Old Spice isn’t a polarizing brand, and McDonald’s is. It should know this, says Napier. Sure, it’s trying to introduce healthier food into its menus, but there’s certainly a population of people who are going to balk, publicly, if McDonald’s tries to push the connection between its brand and healthy, natural food. This social media campaign happened too soon, she says, and no company should open itself up this way when a branding shift is mid-stride.

That being said, McDonald’s could learn something. There isn’t much it can do with the tweet about airborne diabetes, but McDonald’s could respond to complaints about its stores, menu items, or the quality of service. Right now, they should be aggregating data from the failed campaign to see if there are any common concerns that the company can correct, Napier says.

Twitter can actually be a great way to respond to detractors. For example, this month, high schooler Victor Gonzalez tweeted at New England Patriots wide receiver Chad Ochocinco, frustrated that the NFL player hadn’t recognized his fandom despite his two years of avid tweeting. Ochocinco apologized on Twitter then flew Gonzalez to Massachusetts to see the Patriots play the Broncos in the playoffs. The story generated plenty of positive press for Ochocinco, all for the price of a plane ticket.

But companies shouldn’t be caught off guard by the low barrier to entry to a social media campaign, which can seem deceptively cheap and easy. For it to work, companies need to treat it with the same time and effort as other marketing efforts, Napier says. “You can’t just jump on the latest trend, especially when you get into social media.”

Any company that tries to ask, “Hey Internet, what do you think about me?” should be prepared for a mixed response. It might be more effective to ask people, in a creative way, about a specific product or service. Or better yet, make something touching or hilarious, and invite the digital world to share it at will.