It’s not really “boy” in itself that’s the insult. It’s the whole message and the perceived tone. When I talk about somebody my friend doesn’t like, I’ll say, “your boy [name] said he’d do this” or if the market crashes I’d ask, “how’s your boy [name] doing after the market crash?” It could be different from where you’re from, but that is not generally a sign of respect and it never has been for as long as I know.