日語 Japanese Ask Questions Thread2 質問

If you have a question about the language, ask it and fellow 4channers might see it and answer it for you.

Japanese - Ask questions thread
http://dis.4chan.org/read/lang/1174719097/l50

I'm confused about if I should speak casually or politely when I'm with a friend and a superior/boss/teacher

Do I just switch back and fourth between causal speach and polite speech? Or do I just stick to polite? Seems kind of weird to talk to a friend when using masu and desu, heh.