Here's one I've come across in recent months, having starting getting back into improvisational comedy. In Australia, we abbreviate "Improvisation" to "Impro". In America, it's "Improv". Those of us who say Impro have a hard time accepting that anyone would say "Improv"; it just seems a little unnatural to abbreviate something at a point where you wouldn't use a hyphen.
What do you use? Is it Impro or Improv in Canada and the UK? And in other places? Are there other names for it altogether?
PS - For examples of what I'm talking about, see Melbourne impro group The Crew and New York based public improvisers Improv Everywhere.