Ethel: Milkmen are not bound by the same discipline code as are Police Officers, therefore your example, unfortunately, is misleading. Sorry, Ethel.
Hi bednobs:
Although your neighbour did not perhaps commit an offence per se by coming to see you in his uniform, it does seem a bit odd to say the least.
The reason I say that is that Police Officers are subject to certain codes of discipline, i.e. bringing the Force into disrepute etc etc. Such breaches can occur if the Officer is on or off duty.
Therefore, even if he did not threaten you from the perspective of him being a Police Officer, it certainly could be seen as intimidatory that he chose to confront you wearing his uniform.
Police Officers have on many occasions fallen foul of disciplinary matters and, in extreme circumstances, have been sacked as a result.
However, I have no doubt that, were you to formally report him, it would only aggravate your dispute with him, which is in no way excusing his behaviour.
Personally, if it happens again, I would politely inform him that I would not discuss the matter whilst he was in uniform which may have the desired effect. If not, I would just as politely let him know that I was then considering formally reporting him. I think he would get the message.
Good luck.