Why does 80 F feel different when indoors?

Probably the humidity and the movement of air – inside, it feels terrible because the moisture from your skin can’t evaporate due to higher humidity. The air is relatively still too, which means that what does evaporate tends to saturate the air closest to you.

That’s why turning a fan on feels awesome.

Turn a fan on. Outside, 80º F is delightful unless it’s unbearably humid and there is no breeze stirring. Indoors it’s more humid unless you have a dehumidifier running, and there is no breeze. So, as @the100thmonkey suggests, add a fan.

It’s the breeze usually. 80 degrees indoors without a breeze feels awful. I actually hate it when it’s anything greater than 70 indoors but I like warmer weather outside. It’s all about breeze and humidity too.