It was put to both of them that the defeat was among the most aggravating either had suffered in their respective careers: That it had even outranked the Champions Cup last four loss to Clermont Auvergne a few weeks earlier.
“There’s lots of results that have pissed me off,” Sexton deadpanned.
“Even the wins,” Cullen joked.
Sexton saw the funny side of that. His crankiness is well advertised by now. It is a crucial building block in the DNA of a man who has excelled with club, country and the British and Irish Lions. One that has manifested itself time and again on the field.
Teammates are fair game for a lash of his tongue. So too opponents. Just ask Ronan O’Gara. And referees know when they officiate games with Sexton that the perfectionist wearing No 10 will be bending their own ears, too.
He will converse with Romain Poite today with an elevated seniority.
With club captain Isa Nacewa missing training earlier in the week with a bug that invaded his family home, and now repositioned to the wing from centre to make way for the returning Robbie Henshaw, Sexton will be skipper.
“It’s a still a work in progress for me,” said the 32-year-old on the extra duties and his general demeanour.
“When I’m not captain you don’t have that responsibility of talking to the ref but at times in the heat of battle it can get on top of you.
“You probably saw that in the Saracens (quarter-final) I probably let myself down a bit in terms of, you know, getting a bit angry or agitated by some the stuff that is happening. Or maybe a decision I see because I am close to it or I know it is wrong.
“It’s just about biting your tongue. Now I’ve a responsibility to speak to him in the right way. It’s something I’ve had a handful of chances to do with Leinster this year. I’ve done it when Rory (Best) has gone off for Ireland.
“It is something I’ve enjoyed but not something I’m overly burdened about.”
The burden on Sexton and Leinster today is a broader one.
The out-half spoke in the wake of Ireland’s Grand Slam campaign about the wait endured for his first Triple Crown and it is six years now since he was part of his club’s third European title success in four seasons.
“I didn’t think about it like that, thanks for reminding me,” he said, smiling.
“When you are in the midst of winning three previous successes that we have had you think it will be plain sailing every year. Every year you win it you think it is easier and easier but every year you don’t have it it seems to get harder and harder.
“It’s a tough competition to win, especially with the French teams over the last number of years taking it seriously and wanting to win it. We want to get back to a final. That’s our main focus at the minute.”
It’s an understandable strategy. They were left red-faced by Scarlets this time last year. Beaten by 12 points on their home patch by a side that played more than half the game with 14 men and one that never deviated from their expansive, adventurous brand of rugby.
Sexton admitted yesterday that they had been caught by surprise by the Welsh side, whom few expected to register a first ever Celtic League semi-final win away from home, but that there had been failings on their own side besides.
“People thought that might be a one-off and then they went and did the same thing to Munster (in the final) so they proved, and this season again, that they weren’t flukes. They are a very good side and we know about them now, which is an advantage.”
Leinster have been excellent for long spells this season but those semi-final reversals to Clermont and Scarlets have haunted them like the Ghost of Christmas Past. They are demons to be exorcised before they can even think about titles.
Sexton described those defeats as “harsh lessons”. For him and the rump of veterans who had seen it all before as well as the younger guys for whom they were new experiences. The sense emerging from them all this season is that they will stand to them now.
“You don’t always have to lose to win,” said Sexton, “but it does teach you some good lessons.”