Elder Millennial here. I think I just have that “eww pedostache” reaction because, when I was young, such mustache styles were common among middle-aged men who hadn’t updated their styles since the '80s. Some of those men were creepy, so the mustache style became associated with creepy old men. And of course, teenaged giggling among ourselves about “eww pedostache!” really cemented the association.
I’m pretty sure our parents had the same initial reaction when we brought aviator glasses back into fashion. We’ll get over it, the cycle continues.
I use a portable AC - this is different from a window unit. The unit itself stands up inside your room, and it has a flexy hose that goes into a flat panel that’s about 10 inches high and expandable widthwise. You lift the window a bit, put the flat panel in the open spot, then close the window so the light pressure keeps the flat panel in place. It’s all on the indoors side of the screen, so it counts as being inside your house and nobody can complain.
(Assumptions: you have the typical American sliding windows, and your HOA doesn’t have rules about the inside of your house like curtain color or whatever)