The A/C was on at both Christmas parties we attended this weekend.
You're turning on the air conditioner for 80 degree weather? That is utterly ridiculous.
I didn't own either of the homes/buildings that hosted our two family get-togethers over Christmas weekend.
I'm sure they wouldn't appreciate me messing with their thermostat and/or opening up their windows! hahaha
And 80 can indeed be quite uncomfortable, when the humidity is high and you are moving around a lot. It depends on the person.
Right now, with the humidity, we are experiencing a "heat index", which is similar to a Wind Chill up north. It is currently 80.5, "feels like 84". That means that human beings can consider, for all practical purposes, that it IS indeed 84 degrees outside. If you're a thermometer or a plate of water, then it's still just 80.5.
Also, some people simply never open their windows. (We are the exact opposite -- we open them every chance we get) So if they're having 30 people over, plus a few other heat sources, you have to do something to deal with it all. Each person generates 100W of heat, plus human respiration adds humidity as well.