I live in a pretty hot climate, but it’s only really unbearable at times due to shoddy building and bad urban planning. Even then, summer can be difficult.
I can’t imagine what it’s like on the equator, especially in dense urban centres. What’s Mumbai, Bangkok, or Singapore like at the height of the wet season?! How do millions of people function day to day?
I just suffer through any mandatory outdoor events (mostly in silence, but sometimes wailing and profanities are included) and limit myself to activities after sunset, I always keep a bottle of water with me, and I have an hourly reminder to drink when I’m on the computer.