An important thing to note is that Charles doesn’t abide by nicknames and monickers very well. His name is one of the few things Albinus and other handlers could not take from him – it is a core part of his identity in the sense that it serves as a reminder to him both of where he came from and the man he could have been, as surely as it serves as something to develop, so that it can define the man he has become. 

He is Charles Vane and that is something nobody can take away, nor change – so to have that name manipulated or altered by others ( generally harmless things, such as Charlie ) is, by his estimation, a sign of disrespect and an effort to minimize him and the meaning of his name. 

His responses to this are generally sharp and unwise to contradict or ignore – and common enough that the few who do address him by a nickname ought to recognize they are an exception to a ferociously drawn and maintained line. There are three individuals with this power at present.

The foremost among them is Yawi, a former slave woman with a long history with Charles, and the only person who can call him boy and not only get away with it, but immediately have his attention. 

Some may think her nickname for him is Abo as, more often than not when she says it, his head lifts and he immediately responds to her, but that’s literally the equivalent of saying someone’s nickname is You! because they know they’re the shithead being addressed in that particular tone. Her actual nicknames for him are various terms of endearment not uncommonly utilized by mothers overseeing reckless sons. 

Secondarily is Blackbeard, who is the only person Charles respects enough to accept criticism from and any morphology on his name is – generally acceptable. It very much depends on tone – if he feels he is being mocked or derided with the shift, even Blackbeard will be fought on it. And not even Blackbeard can get away with Charlie. He is, however, the only man who can use son and not get himself punched in the face for it. 

That is not to say Charles necessarily sees Blackbeard as a father figure – rather, it is a display of his understanding Blackbeard sees him as a son-figure, and he accepts that the term is not an insult but an endearment, even when it is used in a tone that might incite outrage on account of being scornful or exasperated. Like Yawi, Blackbeard can get away with a fair amount of shit, because Charles understands it isn’t disrespect he is facing, but the frustration of someone who gives a fuck. 

The third, and final party on this list is quite possibly the strangest, and that is Jack Rackham – the only man alive who can call Charles Vane Chaz and not even get huffed at over it. The relationship between both of them is a complicated one to be sure, though I imagine if Jack ever realized how much Charles both trusts and respects him, he’d be downright thrown. 

Regardless of that, it is due to Charles’ unique understanding of Jack that this nickname is permissible – though if it is ever used in a demeaning way, retaliation is generally swift and unquestionably clear that the privilege is temporarily stripped.