Companies in the US usually hold Christmas parties in December. I don’t know about other western countries, but I wouldn’t be surprised if they have similar customs. Normally, one should dress formally in these parties. For man, that means suit, tie, dress shoes, and such.
I didn’t know that when I started working in the US in 1997. And my better half was in Sweden then, so she was not available to make sure I didn’t show up as a slob, which was exactly what I did. I presented myself with a casual shirt, old jeans, and an old pair of tennis shoes, after my coat was handed to the valet. The shirt had vertical red and white stripes all over it. It was not buttoned all the way up, so people could see my Hanes shirt underneath. I may also rolled up my sleeves, just like Mr. Bush tends to do in photo-ops with the American people, to project a rugged and strong image.
Needless to say, I was the only one dressed like that during the party. But that was not the only awkward moment. Again, normally in these parties, alcoholic drinks are provided. I didn’t know what most drinks were. (To this day, I still have trouble telling the difference and the content of various drinks.) I also had trouble pronouncing them. So to avoid trouble, I just said to the bartender: “a Bud Light please”, as if I were a pro. In reality, I would like to know what they were and try some different kinds so I know what I would like in the future. And I don’t like the tepid and yucky taste of Budweiser or Miller. But I was too cool and smooth to admit that.
Fortunately, that party was for employees in the Chicago office, so not too many people showed up. But that experience definitely left a strong impression on me.
PS. PR, I have not forgotten your tagging request. I will post a reply in the next few days.