I think the use of "sir" depends on the person's background culture. If you're from the US, it's probably too formal unless you're in the military or something,

I think the use of "sir" depends on the person's background culture. If you're from the US, it's probably too formal unless you're in the military or something, but other cultures place a higher value on respect for authority. I've had people not originally from the US call me "sir", and while I make sure they know they don't have to, I also don't worry about it.