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'
(..) What is it you're looking for? I just want to find out what's the matter with the salesman's wife. Does that make me sound like a madman? What makes you think there's something the matter with her? A lot of things. She's an invalid. She demands constant care. (..)1954 Rear Window