I’ll make you a bet that you haven’t heard of Chris Messina. He is the creator of the hashtag, and the 1,186th person to join Twitter. This week it was the 10th anniversary of Chris’s creation, the influence of which none of us need to be reminded. But it’s also reminded us that navigating the hashtag (or, if you prefer, the octothorpe) can be a minefield for individuals and brands.

Have you forgotten BlackBerry advertising #rimjobs? Or the good people of Chester literary festival inviting us all to join their #clitfest? Surely you remember #susanalbumparty? There are numerous examples of company marketing and PR departments failing to think clearly about the hashtags they’re using and condemning themselves to internet notoriety. That isn’t necessarily because they failed to see how the hashtag would read. Sometimes a hashtag that seems benign can invite its wilful use for other purposes. Take #McDStories, which was launched by McDonalds to promote the brand and generate positive stories from users. You can probably guess what happened next. A virtual Twitter anthology of negative experiences that took place at the world’s most famous fast food restaurant developed almost overnight.

And of course, it isn’t just the self-made hashtags that have humbled companies. Twitter turned the way United Airlines handled leaked footage of security forcibly removing a passenger from a flight into a firestorm by encouraging users to suggest #NewUnitedAirlinesMottos. Just picture it: “United Airlines: Board as a Doctor, Leave as a Patient.” Embattled Uber meanwhile, currently short of a CEO after Travis Kalanick resigned in ignominy following a raft of scandals, was the subject of a #DeleteUber campaign, which started with a single tweet from a Chicago journalist called Dan O’Sullivan.

A study of online social interactions found that a small group of “seed” users–those with lots of followers–account for a disproportionately large share of viral phenomena. All it takes for a hashtag to become a viral hashtag used by millions of users is for it to be retweeted by a celebrity with a large enough following. This means that for individuals and organisations, failing to deal quickly and decisively with a developing negative hashtag, or failing to consider the potential consequences of creating your own, can quickly become a PR catastrophe.

Ten years on from the realisation of Chris Messina’s “stupidly simple but effective idea”, we should all remember that the hashtag is not a quirk of the millennial generation. It’s moved on from something practical to a symbol that allows for humour, wordplay and even poetry. It’s here to stay. Use it wisely, and you can promote yourself or your organisation incredibly effectively. Use it badly, and you may have to hide under the covers with the notifications on your phone turned off for a while.

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