Why Are You Apologizing for That?

Occasionally, someone will cuss in front of me and apologize: "Sorry, Rabbi" or "I shouldn't speak that way in front of a rabbi."  They apologize as if I am a child or somehow unfamiliar with such language or even view it as somehow wrong/bad. I don't understand why people think that is and it continues to befuddle me - dropping the f-bomb, as uncouth as it is, does not go against Judaism.
 
However, on the other hand, people will either eat unkosher items or discuss eating them in front of me without apology.  Or they may discuss doing various activities on shabbat, etc. etc.  I find it bizarre that they see cussing as transgressive, yet eating bacon, lobster or cheeseburgers as something they are totally comfortable with in front of me....