He is a 'madman' out on the ski slopes. [=he is an extremely daring or reckless skier]
He drives 'like a madman'. [=he drives very recklessly]
a celebrity being stalked by a 'madman'
(..) The human race will have every opportunity to improve. And if they don't? Ask Noah. You're a madman. There were more than a dozen extinction level events before even the dinosaurs got theirs. When the Earth starts to settle, God throws a stone at it, and believe me, he's winding up. (..)2015 Avengers: Age of Ultron