Moving to another country (England) as been quite the eye opener when it comes to culture clashes. I was prepared for the big things like driving on the other side of the road, but overall the English culture is so like the Danish that a lot of small differences sneak up on me. Like how a lot of stores have only one big queue, or that people will offer you tea when you visit but not even think to ask what kind you want because they all drink the same thing (In Denmark if people have tea they will offer you at least five different kinds).
A favorite of mine so far has been the word spastic. In Denmark it's completely neutral if you call someone who actually is a spastic a spastic. That's the name of the muscle disease.
But as I learned after far too long, if is very much an insult in England. When people asked me about my convention experiences I would often mention a spastic girl who came up to my table at most cons in Denmark, and how we got to know each other well enough that once on her birthday she demanded a gift from my table. We joked around and I told her to get lost, at which point she acted up her handicap, flailing her arms about and making stupid voices saying "But I'm haaaandiiiicaaaapped!" and it became a battle of will before I finally gave her a small gift and she returned to normal "Aww, you shouldn't have. Thanks"
I told that story for years in England until someone finally said "You shouldn't call her that if you like her. That's really insulting"
"Stop saying that"
"...But she is a spastic"
So yeah, culture clashes. You learn something new every day.