I've been told that apart from having "stage names" the guys also have other nicknames given to them by their friends and family.

It's a bonding mechanism.

If, for example, you join a football team in Australia, the first thing your team mates do is come up with a nickname. I was told this by a former star football player I once met at a party. His nickname was "the rat". He said he had earned a reputation as a womaniser whilst working is way up through the junior leagues. He was into women like a rat up a drainpipe.