For a man to address another man as ‘son’ is really to call into question the addressee’s masculinity.

Perhaps I should have been more specific and written: For a man to address another man, who is relatively close in age, and could in no way be the other’s father, as ‘son’ is really to call into question the addressee’s masculinity.

Of course, I can only write about this based on my own observations, but the times I have seen this occur, the man calling the other man ‘son’ was doing it to demean the other man. He was not addressing him in a fatherly, mentoring, understanding, caring way, but in a derisive, mocking, disdainful way, very much like the use of ‘boy’, as nancyk points out.

I agree that it also calls into question the addressee’s maturity (“you’re not as mature, wise, knowledgeable, worldly, etc. as I”) and status (“you are beneath me”), but I suggest that such an insult, directed specifically toward the addressee’s role as a male, calls into question his masculinity too – not his gender – and implies that he is more effeminate, thus less ‘manly’ than the addressor – essentially, an insult. I further suggest that such an insult is also a challenge for the addressee to respond in such a way as to disprove such a proposition (usually a physical response is what is hoped for by the addressor), the lack thereof, by default (at least in the addressor’s mind), proves the proposition.

Anyway, that’s my impression, based on the times I’ve seen the word ‘son’ used in a demeaning manner. It may be that such a usage is a regional thing.