I'm frankly not buying this lazy argument. The assertion that "plenty of people are overly polite because it inflates their ego to be perceived as polite" is bullshit. In it's general form it's no more than a convenient tool to disparage those you don't like. Dislike a person but lack a rational or socially acceptable way to criticize them? Easy, just use this prebaked phrasing to cast any exhibited behavior negatively.
Imagine somebody doesn't like happy/serious/polite/flirty/whatever people. Then to them happy/serious/polite/flirty/whatever people are just acting happy/serious/polite/flirty/whatever to be perceived that way as an ego boost. It's an absurdly reductive cynical word game when you need to hate but can't come up with anything substantive. The argument's unprovability short of mind reading and its applicableness to anything (and anything's opposite!) removes any intellectual rigor as it careers completely over the side of "proving" too much. Vacuous rhetorical flourish trotted out in the middle of discussion to target anything the opponent says or does as mere self-aggrandizement.
Seductive if one goes for that kind of sophistry however the reality of human motivation does not resemble this arbitrarily contrived model of, to echo the GP, ego inflation.
Here's the real reason people seem "overly" polite: a combination of cultural norms, fear, being non-confrontational, and power dynamics. As simple as it is.
I know that some people are willing to go through much mental gymnastics to justify hate and derision while seeing themselves as virtuous but had no idea this mean spirited belief pattern was at all pervasive here, however this discussion has led me to revise that belief. It's sickening but rather than continue to get worked up I'll just log out for another 6 month hiatus like I've done before when this community gets a little too high off its own farts. Hopefully things will be better, folks a little less stir crazy in October. Later.