... without hurting their feelings or offending them? I certainly don't want to hurt his feelings and I can't run the risk of offending him ...
Can't imagine what the risk is in someone feeling triggered and offended from the reality of a thing. If no offense is offered, it's done in good faith and done from the heart, whatever misunderstanding comes from inside their own heads. Not your issue.
That said ...
If someone I know or care about, I'd probably offer a couple of suggestions:
1. Reloading is a recipe. With cooking, a bad recipe will simply end up with a dish that won't please. With reloading, however, a bad recipe (matching of X amount of powder to Y primer in Z case) can end up deadly. No way around that.
2. A sit-down watching of your own reloading session, start to finish. You can just chatter away, briefly explaining each step, explaining why the risk exists with getting the reload wrong.
3. A good-quality old/used reloading manual. One of the ones that has a few chapters at the beginning covering the whole of the basic reloading process. Suggest that it be read through at least twice, followed by getting all questions answered, all prior to ever touching a reloading station.
If not someone I care about, really, I might just suggest a good reloading manual and leave it at that. His money. His time. His "kaboom," if he fails to go in with eyes (read: mind) open.
In the end, however, the guy's gonna do what he'll do. If he truly wants no learning, then Nature will assure the learning occurs in its own way, in a manner not up to him. He'll learn, one way or the other. The easy way or the hard. That'll be on him.