Seriously! If you smile, acknowledge someone's existence with a hello or good morning they will think your more than just being "polite" and hit on you. I am married dude I don't want your advances. Idk maybe that only happens when women do it. But I would gather men have been mistaken for flirting instead of being polite as well. I blame the internet and no one understanding how to socialize outside of social media.
Men holding doors for women and calling a woman "miss" or "ma'am" can often be mistaken for flirting. Being nice isn't necessarily flirting. It's just being nice. Perhaps our society is so informal now that true manners are absent in everyday life. Sometimes, it's just the right thing to do when someone is nice when that person isn't flirting whatsoever.
No, manners are not often mistaken for flirtation in today's society, because America is still a very conservative nation. We are a nation of people that are helpful, and people that are polite. Most people know that this is not necessarily to be interpreted as flirtation. Most people are happy to just help each other.