I am often confused on which level of politeness to use between people who are relatively close.
For example, let say I am talking when a friend in Japanese and we use plain form. Although a close friend of that person comes along and joins the conversation. How does the use politeness change between the group?
If its someone I know but would normally use ～ます/丁寧語 form with, would the entire group switch to that? Or would the politeness stay the same between each person of the group?
I have read a different question that was helpful but it is more centered around formalities with work.