Thing is there is a middle ground between being a complete pushover and being an aggressive dictator... it's not always easy to find though and we all tend to naturally sway more towards one than the other. Getting some advice from your manager on how to tackle this sounds good.
I too tend to let minor rudeness etc. go but if you are responsible for health and safety and quality, and this employee is putting themselves/others/the company at risk by his actions I think you are duty bound to say something, all the more so as he is young and inexperienced and may genuinely not be aware of what he's doing. Some tips on difficult conversations/giving feedback I've picked up over the years:
-Try and talk to the person as soon as possible after the 'event'/'incident', but in a calm way and as far as possible in private/on neutral ground. So probably not on a busy 'shop floor' or in front of colleagues but ideally on the same day.
-Address the behaviour not the person, and give specifics. So e.g. saying 'You are rude, I don't like rude people' isn't likely to get good results, but 'I saw you shouting at Julie just now, shouting is rude behaviour and unacceptable' is better.
-Try and set corrections out positively not negatively, saying the behaviour you would like to see and why, not what you wouldn't. So e.g. 'Please remember to put the lid on the bottles of hazardous chemicals when you are finished, this prevents spills' rather than 'Don't leave the caps off the chemicals you idiot, you'll kill us all' 
. Also, just as you would when training an animal or child, try and 'catch' him doing things right and praising him, rather than always correcting (without being patronising of course, I'm not suggesting you clicker train him or reward him with kibble, although my staff do quite like biscuits!) - its human nature to respond better to positive than negative feedback.