When you are trapped in a low SES shithole, it's normal that you wish everyone is in the same shithole as you do.
You don't see flight attendants addressing anyone as uncle or auntie. I stood at the polling station and observed the protocol of the officials. They don't address the old farts who needed assistance as uncle or auntie. What does it say about this double standard ? They understand what is good mannerism, and when they are forced to practice good mannerism, they can execute it to perfection.
Yes, maybe not Sir, but Mister is acceptable because it's 先生 in Chinese, and it's what we learned during primary education.
Addressing someone Sir or Mister who is not related to you by blood is polite, and you accord a degree of social respect to the person to whom you addressed, and most importantly, a reflection of your good upbringing too.
Sinkies are not a bunch of self-respecting animals. The only reason they call somebody uncle is because they want to bring you down to their level as uncle is a derogatory euphemism for old and useless in Singapore. It doesn't matter if you are a Professor or a Doctor, you will be dumped into the same cesspool as those CBL uncles lazing around at the hawker centres and kopitiams. This is the objective - to nullify your advantage over their own low-SES complex.
You cannot make this group of low-SES people high class. Their mission is to make you low class. If you are bothered by them, the best way is to avoid them.