The University I joined as a new grad student treats grad students as both students and employees. So I am confused whether I should behave as a professional colleague or a fellow student with other grad students? I have noticed informal atmosphere within the department(people even use curses in general while talking to professors) but again, sometimes they become very formal and rather act stiff. I am confused.
When in Rome, do as the Roman's do. Observe how your peers interact with their peers, superiors, and subordinates. Emulate them and you'll do fine. Note in what circumstances they are formal and when they are not. For instance, I addressed my professor by his first name in private but by his title in public. Also, don't be too shy to ask someone!