FAIR Work Australia has ordered the reinstatement of an employee who was sacked for telling his boss to "get f ... ed".

Security guard Craig Symes was sacked from Linfox Armaguard last year after he told his manager to get f ... ed, complained about the "f ... ing roster" and then aggressively poked a notice board - all while carrying a loaded gun.

Symes, who had worked with the Brisbane firm since 2000, cracked during a monthly meeting last December after having a fight with his wife before work. "He was frustrated with his wife and, in hindsight, should not have come (to the meeting)," FWA heard.

He abused manager Aryn Hala after being assigned to a faulty armoured van and stormed out.

Symes later apologised in writing but was sacked the next day.

FWA ruled Symes' behaviour amounted to misconduct but found his dismissal was harsh.

While finding swearing at a person was "of a different character" to swearing at an object, or as an adjective, FWA Commissioner Helen Cargill said it was "also relevant to consider the evidence that the respondent's workplace is one in which bad language is commonly used and in which ... employees may have received mixed messages about such use".

She said the swearing was not "overheard by other employees which could have undermined Mr Halas' authority".

Ms Cargill ordered the company reinstate Symes with back pay - less six weeks pay as a penalty.