And when he steps out in public, the comic with a unique twist says he's forced to take his cast of real-life characters with him.
Everywhere he goes, Mario is called upon to do his hilarious impressions of the stars he features in his shows.
"Genuinely," he says, mimicking Miriam's voice, before going on to recall how he had to do a daily performance for the gardaí at Covid checkpoints on his way to work at Today FM in the early days of lockdown last year.
"I was considered an essential worker, so I had a certificate which allowed me to travel in to work," Mario tells the Sunday World.
"Every day there'd be a Garda checkpoint along the way. On the first day when they stopped me, the guards said, 'Right, give us your Miriam O'Callaghan and we'll let you through.
"And I had to go, 'Genuinely guard, are guards getting younger these days?
"The next day I came up and was asked, 'Give us Christy Moore.' So I'm sitting in the car going [adopts Christy's tone], 'How's it goin' guard. Do ya know what, I'm gonna write a song about guards and checkpoints.'
"So I'd have to do an impression every day to get through the guards, probably because they were bored sh*tless looking at people. So I obviously gave them a few laughs.
"By journey 58 I was pulling out Daniel O'Donnell, and then I was down to Willie O'Dea in Journey 94. It was an incredible series of checkpoints."
It's been a tough couple of years for Rosenstock with the cancellation of live shows that account for a huge chunk of his annual earnings.
But while he admits that he's been lucky to have his Today FM radio work and a successful podcast, Mario says he misses performing for audiences.
"I cannot wait to get my stupid f**kin' face out there in front of thousands of people. I was born to do it. My mother said it," he laughs.
"In 2012 I convinced her to come and see my show. She said, 'I've never seen somebody pour so much love into their audience as you did, and everybody in the audience could feel it.' I thought that was a lovely thing to say."
So his mother didn't want him to get a real job? "My parents wanted me to be a barrister because they said I was the most difficult c**t they ever f**kin' argued with in their life," he laughs.
"I am good at taking on the devil's advocate side in a debate, and being a pr**k about it."
Rosenstock reveals that he fell into a successful career in comedy by chance.
"I really absolutely 100 per cent adore it, and I'm completely lucky to have found it," Mario says. "Not all of us go through life finding something, or anything, that we're suited for… and that includes relationships.
"To have stumbled into an area where something naturally in my personality lends itself to being in front of people and sharing funny notions I might have, or funny voices or characterisations, I'm very lucky to have found that. And to be any way successful at it is a miracle and a joy."
The Gift Grub comic tells how Ian Dempsey played a pivotal role in his success.
"Ian heard me doing Starship Compromise on the radio, which featured Gerry Adams and Martin McGuinness touring the galaxy in a starship in search of compromise. In 1997, the only word in our vocabulary was 'compromise.'
"It was all about the Good Friday Agreement and every night you'd hear Gerry Adams being asked, 'Mr Adams, what are you looking for?' 'We're looking for compromise.' It was compromise, compromise, compromise.
"So instead of the Starship Enterprise I had Starship Compromise with Martin and Gerry going around the galaxy trying to establish compromise with different species.
"Ian used to hear this on the way in the car to Today FM in his early days and decided, 'Why don't I have a chat with the guy who is doing this compromise thing.' I sat down to meet Ian and we hit it off.
"Gift Grub became a daily satirical comedy on Today FM, a radio station that had become a phenomenon at the time."
Although they don't hang out together off air, Dempsey and Rosenstock are close pals.
"There's 10 years that separate us and there's a slight brother thing, but there's a slight uncle thing with Ian as well. Definitely in the first 10 years he was a brilliant guide for me in terms of helping me to navigate my way around the industry.
"Ian is wise. You don't stay at the cutting edge of broadcasting for 40 years - and he's still the number one name in breakfast radio - by just being a fluffy fool. Yes he's got a voice like golden treacle, but he's also very sharp.
"Probably what defines him most is his innate decency. That gets you a long way, because everybody knows he's just a decent guy.
"He doesn't f**k people over.
"He's kind of a rare example of one of the good guys doing well and there aren't many like that. He's slow to say anything negative about people, whereas I love having a good bitch, so I'm a little bit of an outlet for him.
"It's a great working relationship."
l The Very Best of Gift Grub Live! Nationwide tour will kick off in March 2022. Tickets are now available through ticketmaster.ie