Most of the male characters in The Big Sleep like to think of themselves as macho. There are constant fistfights, arguments, and shootouts that arise out of this sense of challenged masculinity. They talk tough, hit hard, and never apologize. If we're to take Chandler's view, that's pretty much a requirement for surviving in 1930s L.A. The streets are mean, so the men must be meaner.
The men in The Big Sleep are forced to talk tough and act tough because it's the only way to survive in the gritty streets of L.A.
Marlowe's tough guy exterior hides an inner romanticism that he hides from the rest of the world.