I get called sir all the time. Such as, sir can I help you across the street. Or sir, are you okay you look a bit ill.
I think in your case that there is definitely a racial overtone. There is not an influx of young sub bottoms, I think there has been an influx of people who no longer know where boundaries should exist. I Politeness, courtesy and respect for others has been on the decline for a long time and the current political leaders have taken the downhill slide and made it into a avalanche.
I am sorry that you are falling victim to other's ignorance. If their scene is the kind of interracial degradation you believe it to be, I would suggest you be blunt and just say at the first "sir" that you are not into degradation, so if that is what they are after, they need to troll other waters,