It takes years to build a professional reputation, and just moments to destroy it.

Here are five career killing moves and examples of people who have made them.

Throwing a tantrum. It might seem like a good idea to scream at your boss or coworkers in front of the whole office, or maybe storm out yelling something like “Who needs this s*&^!” You might even cry, scream and throw a few things. But you can’t take that kind of thing back. Word gets out, and before you know it, you’re persona non grata at every company you want to work for.

Example: It’s been suggested that infamously short fused Microsoft CEO Steve Ballmer, who retired in 2014, was actually fired in part because of a tantrum he threw in front of the board. Granted, he’s worth more than $20 billion* and owns the Los Angeles Clippers. But you don’t have $20 billion and a sports team, so it would be a riskier move for you to do this.

Behaving badly on social media. Venting about your current boss online is the biggest turn off for most hiring managers, while getting into overly heated arguments doesn’t make you look very good either, and one recruiter I spoke to said bad spelling and grammar turns her off completely. Venting about bosses is definitely the worst. People like to argue that their social media is private and none of any employer’s business, which is fine, as long as you realize that thinking that way can cost you. (And, as I have said before, don’t think your privacy settings will save you. It’s a small world.)

Example: The most famous example is probably this woman, who called her boss a pervert on Facebook, forgetting that she had added him as a friend. His response was priceless – “You’ve worked here for five months and haven’t worked out that I’m gay?” – Obviously she lost her job.

Being mean. Always be nice. You never know who is watching and who might post something to social media that might go viral. It’s not always easy to be nice. Most of us lose our cool sometimes. Then there are those who lose it in dramatic fashion.

Example:Earlier in 2014, Kelly Blazek, owner of the Cleveland Job Bank, who had previously been named Cleveland’s “Communicator of the Year,” lost all credibility and was asked to return her award after she angrily rejected a job seeker who asked to join her board, sending a bizarrely nasty message that the job seeker posted to social media and that went viral.

Committing a crime. Hopefully you’re not going to commit a crime, but be aware that, should you suddenly get the urge to do so, it could destroy your career. These things have a habit of circulating all over the internet these days, and mugshots have been known to go viral.

Example: Again, I’m sure YOU would never do this, but in 2011, hundreds of people participated in the Vancouver Stanley Cup riots, vandalizing property, setting cars on fire and basically being terrible people. Three years later, a total of 887 criminal charges have been laid against 300 people whose pictures have circulated all over the internet. Michelle Scarce is just one rioter who lost her job after her picture appeared on social media.

Behaving totally inappropriately. It’s true that lots of people who don’t know how to behave have careers. But once in a while, doing or saying the wrong thing can pretty much destroy your reputation. Like what? Like getting drunk at the office party and getting off colour with your choice of karaoke song, as this journalist recounts in his own personal cautionary tale.

Example: And in another example, you might have heard about young Sun News journalist Vandon Gene who was sent to cover the Ottawa shootings on October 22, 2014, and who, upon meeting Anderson Cooper, who was also covering the event, decided it was a good time to ask for a picture with the famous anchor. Cooper refused and berated Gene for having no respect for the situation. Gene later took to Twitter to accuse Cooper of “exploiting” the Ottawa shootings, then thought better of it, removed the tweets and apologized. But the damage was done and Sun News has cut ties with him. He doesn’t deserve to be punished for the rest of his life for making a dumb mistake, but his actions will undoubtedly colour his reputation for quite a while.

Beware – and don’t make these same mistakes.

*thanks to commenter liQuid03x for pointing out that I had written “$20 million,” a pittance compared to Ballmer’s actual worth

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