Corcoran headed the team which garnered millions of followers across their Twitter, Instagram and TikTok channels.
He wrote: “Building one of the most successful brands on social media [...] is still not enough. There’s challenging and pushing a team to hit the next level [...] and there’s being a d******d and making it personal in its delivery.”
Corcoran also alleged that HR had protected directors, rather than employees.
He wrote: “Even if a director verbally abuses people in public or gets so far in another manager’s face shouting in a professional setting, this tiny, tiny human will always be protected.
“Why? 20 years of ‘loyalty’ or institutionalised and conditioned by those above them…who knows”
He also warned employees not to regard their manager as their friend and said "everyone has their own agenda".
Neither Corcoran nor Ryanair replied to a request for comment.
Read more: What is #WorkTok?
Social media has given ex-employees new power to damage employers’ reputations, according to Simon Jones, director of Ariadne Associates.
Speaking to HR magazine, he said: "In the past, disgruntled ex-employees might have bad-mouthed the company to friends and family. Social media allows those views to be amplified worldwide and can create reputational damage for businesses.”
Ruth Cornish, founder of HR consultancy Amelore, said when ex-employees post disparagingly on social media, HR teams need to take swift action.
She told HR magazine: “When a current or former employee says or implies negative things on social media, it can be extremely damaging for an employer in terms of brand and reputation.
“Often a conversation can appease the situation and the employer can ask for the post to be removed.”
In some cases, she said, employers could consider legal action.
“If they consider it slanderous, employers could threaten legal action against the ex-employee. Senior employees in particular may be subject to contractual clauses or polices that require them to keep certain information confidential post employment.
“Likewise it is an expectation that managers and leaders don’t do their dirty washing in public.”
Jones said the posts show the importance of investigating complaints and conducting proper exit interviews.
He said: “Unless someone has breached a settlement agreement there is very little a company can do to prevent such posts, but they are a reminder that HR should never brush employee concerns under the carpet.
“Investigating or resolving some of the issues before the employee left might have avoided such public criticism.”