I see that you're getting flak over the way this was asked. I agree it comes off as a little "archaic".
But I also empathize with the underlying premise of your question, and think it's perfectly valid.
In my own experience, I bristled (to put it lightly) at being called my childhood nickname into adulthood. I started hating it when going through puberty. Repeatedly confronting the parent in the style of a "good man" (calm and business-like) didn't work. But finally doing so in the hyper-aggressive style of a "real man" did the trick.
(And that's an important distinction. Think of attributes popularly used to describe a "real man". Hyper-aggression as in action movies, the emotionally dysfunctional detective, songs about ramblin' man, Freebird, etc. Generally, self-destructive, socially dysfunctional, unpredictable, unreliable, violent. Then do the same for a "good man". Notice how they differ. My own nature tends toward "real man" but I constantly strive and struggle to be a "good man". Mostly because I've seen up close and personal, how destructive a "real man" often is.)
I'd recommend letting him develop in the "manliness" department however he's going to do it no matter what you do or say. What I've learned in my many years is that gender identity and sexual preference, are deeply baked-in at a genetic or epigenetic level, and have more to do with levels of the complex brew of hormones that are present during development.
We all have testosterone and estrogen, for example. They are all present to varying levels in everyone, man or woman. Tweak that balance, and everything changes.
No nickname or lectures in the world will change that, but not supporting him no matter what his personal choices are, as long as they aren't socially harmful, will absolutely determine whether or not you have an ongoing adult relationship with him at all.
You aren't going to get a persistently "rough and tumble boy" who loves to sit on their friends and fart on them - to act with deep empathy, sensitivity, and social responsibility - any more than you're going to get a sensitive bookworm who identifies more with his female friends, to be like a hard-ass stoic John Wayne fictional character.
I don't think it would matter what the nickname is, or whether it sounds tough and masculine, or feminine. Either way, kids need to leave certain markers of childhood "behind". A childish nickname - or any nickname associated with one's own childhood - being high among them.
In my case, once puberty hit, I just wanted to be called by my freaking name.