An etiquette expert has revealed the one thing you should never say to your colleagues. 

According to Amanda King, an etiquette specialist from the Australian Finishing School, you should never greet your colleagues with "hey". 

Speaking to Nine Honey, King said the greeting blurs lines between professional and social relationships especially now a lot of companies are using online tools like Slack and WhatsApp. 

The expert said: "A greeting helps establish the tone for the remainder of the conversation and can determine the impact your communication has on the receiver. 

"Respect their name and do not start with nicknames." 

She went on to say: "You may start your email with 'Hi' in most professional situations, unless you need to be explicitly formal in the communication. We recommend in formal situations where you might not know the receiver on a first name basis, use 'Mr' or' Ms' along with the recipient's surname." 

Amanda King said the term "blurs lines" between professional and familiar relationships. Photo / Instagram @australianfinishingschool 

The Daily Mail reported King's advice comes after a man took to Reddit to share an exchange between him and his boss in which "hey" triggered the boss to respond sharply. 

"Hi Shreyas, my name is Sandeep. Please don't [use] the word 'hey'. It's offensive for me,' the boss said. 

"If you cannot remember my name, simply use 'hi'. Other words you should never use professionally: 'Dude', 'man', only 'hello', 'hi there', if you are not targeting a wide audience in a mail to senior [people] to you. 'Chap' or 'Chick'. Thanks." 

Users of Reddit quickly replied to the man saying "how is 'hey' considered unprofessional when 'hi' isn't". 

Another said the boss seems more offended by being "dragged into the same class as his staff". 

King agreed with the boss's reply and said "once in conversation we advise good morning or afternoon". 

She went on to say while people have become more comfortable and confident in their workplaces, "basic etiquette should still be adhered to".