Sa Bum nim until they do masters grading, when it's master so-and-so. Also as Sir/ma'am. Lau if I like, but I would never call Master Zamparelli by his first name. It's probably because my instructor is more of a friend than the master, so if it's a non MA social event, he'll be Lau. Having said that, I know a Cho dan who I doubt I will ever call them Sa bum Nim. They are not an instructor, and thats what it means to me. If I see a school teacher walking down the street then I will call them Sir/Miss. If I am good friends with them I may call them by their first name, but in a learning environment they are still Sir/Miss. Oops, there I go again, I should stop talking.