Machine Gun Kelly is a perfectionist.

The 32-year-old musician's close pal and musical collaborator Brandon 'Slim' Allen revealed that Kelly is the "hardest critic" to please, when they put on a show.

He told Billboard: "Kells is the hardest critic. We’ll have an amazing show, 100,000 people, and he’ll find the one thing that didn’t go right.”

Kelly agreed but added: “I also hate perfection. So I don’t know why I get so anal about [everything]."

While Kelly and his band - guitarist Jus Lyons, drummer Rook, bassist Baze and keyboardist Slim - are playing huge arena shows these days, he used to do anything for attention when they were performing in smaller venues.

He said: "I would take my clothes off and just be in my boxers, and I would just have this lanky, stupid body. But it made people stop.”

And, along with performing at the Grammy Awards and headlining Madison Square Garden, Kelly's hopes for his career include playing "underwater".

He said: "I wanna perform on all seven continents. And then I want to perform in the ocean. Like, underwater. I don’t think anyone’s done it.”