Is it considered offensive to address one's seniors by name in the US? In my country (India), there are several implicit norms that need to be followed by almost every one.
Among all, an important norm is that juniors does not address their seniors by name. It happens in both students' circles and faculty circles -- thus, even junior professors would not address senior professors by name.
Recently (in the US), a female assistant professor addressed a male associate professor by his name. It is the first time ever I saw an incident like this personally. I personally considered it as an offense to the male associate professor.
So, I am wondering whether it is a norm in the US to address seniors as &quot;sir&quot; or any other respectable salutation instead of addressing by name.
Note: The question is broader than only addressing a professor.
No, in the US, it's usually not rude to address people you know more than in passing (e.g. are colleagues, classmates, or in their class) by their first name. NB: The question isn't &quot;How should I address a professor?&quot; it's about general rules and behavior, especially (my interpretation) the same university.
In the US, professors, staff, and PhD students would address everyone on their own &quot;level&quot; by their first name. In every department I have encountered, anyone in any of those groups would address each other by their first name, but as others have pointed out, occasionally Master's students maintain a bit more formality.
Occasionally, some professors prefer their undergraduates (especially in large classes) to use their title, whether &quot;Professor,&quot; &quot;Doctor,&quot; or &quot;Mister/Miss/Mrs.&quot;
All undergraduates would use first names, and would almost always use first names with staff and graduate students they are familiar with.
However, it's typically considered polite to start using the title (for faculty, and maybe staff) and to only use their first name when invited, which most people in academia in the US do right away. Often, the convention is people sign their emails how they want you to address them. In my experience, it would be a raised eyebrow to use a first name where it was &quot;incorrect,&quot; but would really only elevate to &quot;rude&quot; once someone has consistent disregarded someone's expressed wishes.
In regards to your example, it would strike me as incredibly rude if  a professor took offense at another professor by using their first name.