Funny you mentioned it, After finishing the mages guild I was walking around in Mannimarco's robes with his staff in my inventory. I was walking around the imperial city market district and I took it out coincidentally as I was passing by this mage in white robes. I never attacked him, but for some reason he was threatened and attacked me first. The guards killed him but I thought that was a nice touch.
A little off-topic, but I'm almost positive you're talking about Ontus Vanin, the retired Mages' Guild member. He's subject to a bug that makes him dislike Mages' Guild members, and that disposition drop is multiplied by your rank in the guild. Since you would have to be Arch-Mage to have Mannimarco's robes and staff, it's pretty much a given that he would attack you on sight, whether or not you had those items. So, unfortunately, that's not an example of NPCs reacting to the clothes you're wearing--in fact, the King of Worms' robes don't even cause guild mages to refuse to speak with you the way regular necromancer robes do (at least, not in the vanilla game).
However, I think this just highlights the need for that kind of interaction in Skyrim. It makes no sense for an encounter like this to be due to a bug rather than deliberate planning by the game designers, and there should be even more things like it.