I hate when people say "dont call me sir (or mam) I'm not old" cause my immediate response is always yes sir or yes mam lol. I was raised with good manners so it's kind of a habit but I also do it just out of respect for people.
I will say it has helped me out in a lot of ways.
I just tell the the person, "sorry, I am from Texas and I was raised with manners." I figure it is a polite way to insult their lack of manners.