I never attended one; the closest I got to that celebration was when I was taking an English (conversation) course. Our teacher asked us to come to the class with something that, at least, resembled the real MCoy.
At the end of my workday I went right to my wardrobe and tried to find something that fitted the occasion, nothing, just a black-and-white shirt (black with white stripes or vice-versa? don´t know up to know.)
Problem was, our teacher rang everybody and said to go in the usual clothes, no need to get there in Halloween costumes! except, that she forgot me!
Ha ha, you can imagine when opened the door and everyone was clothed as usual, my luck was that I had just found a Jeans pants and didn´t took a broom to the class!
I think that day made me an unforgettable guy there!