The schmaltzy congrats he gave PA Melissa Addington-Smith - on her engagement to financial unit consultant Peter Corbyn - included a round-robin e-mail to all staff informing them of the happy news.
'All part of the family atmosphere,' he wrote, leaving ex-Shandwickites across the capital crying onto their P45s and bemoaning the lack of family atmosphere when they were given their marching orders.
'You should be proud PR has come of age,' Byrne tells PRWeek in his defence.
'PR was thought of as froth and frippery, but agency chiefs are now asked to take part in a slot normally reserved for CEOs of FTSE 100 companies,' he adds.
Byrne also seems to have got away with describing Square Mile managing director Susan Ellis and youth marketing chief Christine Warren in the old-fashioned terms of 'feisty' and 'sassy lady', respectively.
'Sassy is better than feisty,' says Ellis, 'but then I am feisty - I'm from Yorkshire.'
Warren, the founder of R1C and passionate clubber who merged her firm into the Shandwick beast a year ago, is chuffed to bits with her descriptor: 'Sassy says cutting-edge and out there, assertive and fun. That's me.'