There have been the broken arms -- five in total. He has broken his left arm four times and his right arm once, misfortune which would have forced many to think about packing it in. Not him, though. He has been in and out of the All Blacks, painful in itself, which he believes his many injuries have given him the mental strength to handle. And there is the school of hard knocks, which the now 33-year-old encountered during his introduction to the game in Southland before he made his way north to Christchurch.
All things considered, Flynn, who will leave the Crusaders for Toulouse in France at the end of the season, has had a colourful career.
He isn't one to get ahead of himself, which is why this week he was wary about talking up the Crusaders' chances against the Sharks in Christchurch tonight, saying simply the team had prepared well over the past fortnight and it was now up to them to get the job done in order to make their first Super Rugby final since 2011.
He was, however, in the mood for some reflection, including his arrival at the Crusaders in 2002, his respect for his rival du Plessis, and the things he will miss most in Christchurch.
Asked if after the fifth broken arm he might have considered a new career path, he replied: "Never. You wonder why injuries are happening but it allows you to get a bit of mental resolve and I think it's been the making of me in terms of being able to handle injuries or non-selection or stuff like that.
"It gives you the resolve to keep boxing on. I think it's completely the other way, I never had those thoughts. We're pretty lucky to be doing what we're doing."
Flynn arrived in Christchurch as a 21-year-old not quite sure what to expect after representing Southland for two years. They did things the old-fashioned way in Invercargill in those days -- young players were forced to scrap for everything -- so his arrival at Crusaders' HQ was eye-opening on several levels as front rowers Greg Somerville, Greg Feek, Mark Hammett and Dave Hewett took him under their collective wing.
"As soon as I came to the Crusaders I actually found it quite unsettling in terms of how much they were prepared to help me. I had come from an environment where you learn by getting a hiding and then all of a sudden I was then given all this knowledge ... I was like 'what's the story here, what's the catch?'. It's always been like that since I've been here."
Flynn's experience is probably the main reason he has been given the starting hooker's role against the Sharks and he has nothing but respect for 30-year-old du Plessis.
"He's a pretty fierce competitor, he's been one of the best in the world for a couple of years and he's also come back from a pretty serious neck injury so that deserves respect in itself. As a footy player and as someone who thrives on challenges, it's pretty exciting to come up against the best and that's what you mark yourself on."
Flynn has always been a forthright character, one who is prepared to ask difficult questions if they are required, but he also has a finely-honed sense of fun.
One of things he will miss when he leaves for France, and with the competition starting in mid-August, Toulouse want him there as soon as possible, is an annual "spud competition" which has been a tradition for the past five years or so for Flynn and several of his mates, including teammate Dan Carter.
The competitor who grows the biggest yield of potatoes from a single plant takes the title. It is a social competition which Flynn has yet to excel in. "I'll definitely miss that. I think the boys are holding a spot for me, they're not going to just give it to anyone while I'm away.
"I have been horrible for the total of five years. I needed this year for a bit of redemption, but it will have to wait.
"DC [Carter] is terrible as well. I think, putting so much focus on the footy, spud growing definitely takes a bit of a hit."
Crusaders team to play the Sharks at AMI Stadium today, kick-off 7.35pm is: Israel Dagg, Kieron Fonotia, Ryan Crotty, Dan Carter, Nemani Nadolo, Colin Slade, Andy Ellis, Kieran Read (c), Matt Todd, Richie McCaw, Sam Whitelock, Dominic Bird, Owen Franks, Corey Flynn, Wyatt Crockett. Reserves: Ben Funnell, Joe Moody, Nepo Laulala, Jimmy Taufua, Willi Heinz, Tom Taylor, Johnny McNicholl.
Sharks: SP Marais, JP Pietersen, Paul Jordaan, Frans Steyn, Lwazi Mvovo, Pat Lambie, Cobus Reinach, Ryan Kankowski, Jean Deysel, Marcell Coetzee, Stephan Lewies, Willem Alberts, Jannie du Plessis, Bismarck du Plessis (c), Thomas du Toit. Reserves: Kyle Cooper, Dale Chadwick, Lourens Adriaanse, Etienne Oosthuizen, Tera Mtembu, Charl McLeod, S'bura Sithole, Tonderai Chavhanga.