Hi everyone!
One of my English teachers says that it is rather rude to answer "yes, of course". The situation was the following:
A foreigner asked if a monument depicted some national celebrity, and a guide answered "Yes, of course". The foreigner took offense, for it sounded to him like "Yes, it is, and you are a fool to ask of it". 
Is it really so? What other ways exist to express in English "Yes, you are absolutely right"? 
Thank you for your help.