In December 2013, US communications director Justine Sacco sent a tweet as she boarded a flight: "Going to Africa. Hope I don't get AIDS. Just kidding. I'm white!"
While in flight, the tweet circulated the globe and tens of thousands of people responded with outrage at the racist tweet. The hashtag '#HasJustineLandedYet' began trending worldwide. She subsequently lost her job, and was trolled by thousands of people.
A hugely regrettable mistake for Sacco, made particularly surprising as she worked in communications. But one which illustrates just how badly a misplaced tweet can affect your personal brand.
Conversely, take a look at homeless 20-year-old Jordan Lockett, who's heartfelt handwritten CV was posted on Twitter in July. It was retweeted thousands of times and led to him having meetings with people offering him work.
We all have a personal brand. Not everyone may wish to acknowledge that fact, or do anything about it - but it's there.
Your personal brand is how you appear to the world, and how you sell yourself to the world. Therefore, it stands to reason that a strong brand is preferable to one that is unlikeable.
What affects your personal brand? It's in the way you talk to people and the way you dress. But social media provides a means by which your personal brand can be out there in front of hundreds, thousands, perhaps even millions of people, at any time.
Get it wrong on social media and you can potentially get it wrong in front of thousands. Social media fails don't just happen to celebrities accidentally posting intimate pictures or footballers making offensive comments. We are all capable of posting material that reflects us in a very, very bad light.
Why does it matter? Well, if you're applying for a job, there is every chance that they will check out your social media profile. If you're looking to join a club, speak at an event, get voted into an elected role, there's every chance that your postings will be scrutinised. But regardless of that, why would anyone want to be viewed in a negative light?
Let's take this right to the basics. The names you use are important. That stretches from your email address to your Twitter handle. @babycakes987 is out; @firstnamelastname is in.
And then we get to the content. If you're thinking of posting something, read it twice and edit it before you post. Keep in mind that others are reading and never write something in haste.
Remember the story of 22-year old Connor Riley, just another young person who had been offered a job for which she had mixed feelings. Feelings which she voiced on Twitter: "Cisco just offered me a job! Now I have to weigh the utility of a fatty paycheck against the daily commute to San Jose and hating the work."
A Cisco employee tweeted back, "Who is the hiring manager? I'm sure they would love to know you will hate the work. We here at Cisco are versed in the web." Oh dear, Connor.
The pictures that you post also say so much about your personal brand. Is there alcohol (or worse) in view? Are there any photos of - ahem - unusual social situations? Take them down, they're ready and waiting for someone to draw attention to them, probably when you least want it.
And react carefully. You're not Kim Kardashian or Azealia Banks, and flaming isn't cool. You could easily give the wrong impression if you lash out at someone emotionally. Never react to others' posts immediately. Wait and think twice before you respond.
I've focused a lot on the caution side so far. But if you were only to think in such terms, your online personal brand stands a chance of being pretty dull. It's a tough line to walk: how to be inoffensive while being interesting, witty and opinionated in a way that enhances the way people see you. Tricky... but not impossible.
Look at Taylor Swift. She is masterful in the way that she uses social media, using it to portray herself as approachable and unpretentious, but also someone who has strong points of view on issues that she cares about.
Think about your own talents and interests. Define your area of expertise and identify your passions. What makes you different? What are the things that interest you enough to talk about more than anything else? Once you have those subjects in mind, put in some research and develop your insights on them.
It's not a long leap from there to being able to develop a core message or mission statement.
It's useful to look at how other people behave online, and from there see if you can work out their own mission statements. Take someone like Hillary Clinton, or Boris Johnson. What kind of personal brand are they trying to create, and how do they achieve it?
It's not an accident that they come across in the way that they do - it's all been well thought through to achieve the very specific effect that they want to achieve.
You can do it as well. And let's be clear, I'm not talking about lying or concealing your true identity. Think of it as being the best version of yourself.