Yep, this behaviour needs nipping in the bud before anyone else gets... nipped in the bud!
Clear & *consistent* boundaries are vital with horses & I would be teaching him that he's not to come within about 1' of me without an express invite, and that he is to keep his nose to himself at all times. If he takes it as a game or challenge you're maybe not being firm or consistent enough, or your timing is out - horses are more likely to misunderstand & play 'tit for tat'(well, hopefully not tit..
) if you *react* to their 'wrong' behaviour with punishment after the event, but if you can set it up so he 'punishes' *himself* for it - eg. You're waving your arms around 'randomly' and he gets in the way, you happen to be holding something pointy or prickly when he shoves his nose on it... he'll realise this isn't a good idea.
Another thing to pay attention to is reinforcing Good manners, especially if they're exclusive to the Bad manners - eg. He won't be nipping you if you're reinforcing him for 'respecting' your personal space & keeping his nose in & down. You can use food treats or anything else he really likes(like a good rub) as positive reinforcement, but whatever you use, it's important NEVER to reinforce 'rude' behaviour, even if it's in conjunction with something Good. Horses learn from association, so *whatever is happening at the time of* a reinforcement or punishment... which I think is a big reason why so many people have problems with food treats & horses reacting badly to punishment.