Should I use -Sensei (先生) to refer to a teacher if they aren't my teacher?


Does it make a difference whether they teach at my school, even if they don't
teach my class?




As long as you are interacting with the said person in its role of teacher,
you should use 先生. Meaning that you won't if the person is your friend, family
member, partner or any other relationship that doesn't involve its teacher
job, even though it can still be used in this case as a joke, irony or to
emphasis the teacher position.

