Leavy is now proving he's got qualities to make it big with Ireland: O'Mahony
It is something of a back-handed compliment, but one international back-row forward describing another as a "pain to play against" is high praise indeed.
Peter O'Mahony and Dan Leavy followed similar career trajectories as schools stars turned U-20 captains and now they are lining out together.
One is quintessentially Munster, the other is as Leinster as Leinster can be.
They're getting on just fine.
On Boxing Day, the Munster skipper got a taste of what his Ireland team-mate can do when he is at his best.
Leavy was in dominant form at Thomond Park and he's beginning to show signs of those performances on the bigger stage as he gets used to his surroundings.
"He's been very impressive," O'Mahony (below) said.
"I can speak from first hand, he's a pain to play against, and that's a great compliment from a back-row.
"And he's been super to play alongside the last few weeks, he's been a great voice.
"He's one of the young fellas to come in but he's doing an incredible amount of learning quickly, and I'm doing some learning off him as well.
"The way he plays the game, it's obviously very physical and intense but it's very smart, and he's been brilliant for us the last three weeks."
Off the pitch the 24-year-old is not afraid to say his piece.
"He's well able to get stuck in and give his opinion and that's important for guys to grow up quick and if they've something to say, to say it, but obviously not if it's not relevant," O'Mahony said.
"That's something that they've copped on to quickly, that if they've something to say they'll come across and have a word, and that's invaluable for a group to learn like that quickly and he's one of the guys I've been very impressed by."
As a provincial skipper and one of the senior men in the Ireland squad, O'Mahony has been impressed with how the young guns have adapted to the international game.
Along with Leavy, Jacob Stockdale, James Ryan, Andrew Porter, Bundee Aki and Jordan Larmour are all in the infancy of their international careers, but they are coping well and find themselves on the cusp of history in their first full season on this stage.
The Six Nations title is potentially on offer today, the Grand Slam could be secured in a week's time, and it would be understandable if they were struggling with the high stakes.
Yet they have looked so comfortable at this level to date, adapting to the challenges put in front of them well. None of them have lost an international yet and O'Mahony does not see any signs that the pressure is getting to them.
"I don't think it will," he said.
"It will be there in the back of your head, obviously, but we're going through each week and every game is massive for us, especially the last three games.
"(In the) Six Nations, as soon as you lose one you're under big pressure.
"So we've had that pressure from day one, so this week doesn't get any different from what the lads have experienced for the last three weeks.
"We've just to got prepare well in the run-in again because we've had this pressure, this internal pressure that we put on ourselves and the external pressure that gets put on us as well, and the lads have experienced that in the last few weeks.
"It doesn't change.
"This game isn't bigger than last week and it won't be bigger the following week. They're all massive games."
As Munster captain and one of the main leaders in the Irish squad, O'Mahony acknowledges his own role in setting that particular tone.
"You try and take a bit more responsibility as you get a bit older," he explained.
"We've a lot of young guys now who are taking a lot of responsibility, they're coming in and it's like they've had 15 or 20 Tests under them already.
"It's incredible the way they carry themselves and that kind of a boost to the squad with however many young fellas we've got of the last 12 or 18 months is invaluable."