The Irish actor - best known as Sherlock's nemesis Moriarty in the hit BBC show - was joined by the cast of the comedy for the premiere in London's Leicester Square tonight.
Following on from the success of films like The Hangover and Bridesmaids, the new Irish comedy is about a group of friends who are reluctantly forced to go on a stag party against their will, and end up rediscovering their friendship.
Scott revealed: "I think what people find a bit scary is the idea of stag and organised fun and people being tied to lamp-posts and all that kind of stuff.
"So this is about people that don't really want to go on a stag, but at the end of it understanding what a stag do really is - it's about male friendship and reconnecting. It's not about your life ending because you're about to get married."
Director John Butler agreed: "This is The Hangover cure. I think The Hangover's a great film but this is for people who don't want to go. And what they're forced to do, in terms of embracing traditional masculinity, it helps them to learn stuff. And it's funny."
Peter McDonald,who co-wrote the film with Butler and stars as party animal The Machine, said: "A lot of people go on stags and hens. I've been on many in my time, and everyone gets drunk. But they are a ritual. And we want you to explore that ritual. Does it have a meaning anymore?"
The Stag tells the story of Davin, played by Scott, who agrees to be best man for his best friend Fionnan (Hugh O'Connor), despite being secretly in love with his fiancee, Ruth (Amy Huberman).
He organises a stag party comprised of camping and hiking in the countryside, despite neither he nor the groom really wanting to do it - unlike The Machine, Ruth's crazy brother, played by McDonald, who she insists should go along.
Scott revealed he was keen to do a comedy to shake off the character of arch- villain Moriarty, who has made him famous all over the world.
He said: "I've wanted to do a comedy for a long time. I've been doing some quite dark work in recent years, so I wanted to do a comedy and I wanted to work in Ireland and I wanted to work with my mates."
And McDonald thinks Sherlock fans will be surprised by the film.
He said: "Andrew, I've known a long time, and he's an amazing actor, and he's very, very funny in person.
"Because of Moriarty in Sherlock he's known as playing a very intense character. But I knew his comedy chops were as sharp as could be."
:: The Stag opens in cinemas tomorrow.