While culture is frequently exhibited in behavior (I still don't feel comfortable wearing a hat indoors but it's no longer universally considered rude), more often than not, the issues arise through language. When my brother in London told me he was getting pissed, I felt very uncomfortable until I realized he was "getting drunk". When I first moved to the Pacific Northwest, I couldn't help but laugh the first time a lady offered me a "pop" because I was used to little kids referring to "pop" and adults referring to "soda". I heard a grown woman talking like a little child.
Perhaps one of the worst issues with culture arose in Texas when I first realized that my friends' use of the word "nigger" was offensive. Vowing to not be a racist, I altered my vocabulary to show proper respect. This shocked my mother. She, to her credit, informed me that the word I was looking for was "black", not "negro". That I could have thought "negro" was acceptable tells you a lot about Texas culture (and perhaps why so many Texans like Bush).