It is a typical slang word meaning man. It could be used as a derogatory form of naming a person.
But, in some situations, it could be interpreted as a very masculine man, one that a woman is attracted to.
Negative: "ese lo que es es un macharran" - "that guy is just an asshole"
Positive (from woman to a man she likes): "lo que necesito es un macharran como ese que me caliente por las noches" - "what i need is a man like that to keep me warm at night"