I know that Bangkok heat well. That humidity is a killer.
From an observing point of view, I think most people are more concerned with cold than heat. These threads come up all the time, but I can’t remember one asking when is it too hot to observe.
It seems that way. IMO, heat is easier to deal with-- getting ready for cold takes extra equipment (warm clothes), takes longer (I've said before that my "grab n go" is spoiled in winter by 10 minutes of bundling up in clothes), you can only put on so much before you can't move (and as has been noted before, face and hands can be an issue), and all the cold-weather gear can make it hard to carry and handle equipment. "Too hot" can be handled with as little lightweight clothing as possible, cool towels, fans, etc. Being too hot is uncomfortable, but being too cold is uncomfortable and a hassle*...
Well, it is snowing here now, but I've still been going out when the skies open for looking at the moon. Never had to deal with extreme cold. I keep cozy with my wool socks, wool base layers, wool gloves, then lined pants and comfy jacket, and a wool buff around my neck and face, and always piping hot coffee in my thermos.
One of these days when I own a larger telescope I'm sure I'll overstay my night in the cold.
Yes, I can dress up pretty well. Usually consists of 2-3 base-layer leggings, track pants or whatever will fit over top, a base-layer top with a fleece jacket, two pairs of socks + fleece boot liners, thin glove liners under thick ski gloves, a neckwarmer or scarf if needed, winter coat, fleece earwarmer or earmuffs under a Sherpa hat, and maybe snowpants if necessary (haven't needed them yet this year). For the most part that keeps me warm enough, except sometimes my feet still get cold, face is problematic, and hands if the thick gloves need to come off and it's too cold.
When is it to cold to observe?
When my glass of Scotch freezes!
I like the way you think; I think this is my new metric...
*This is pretty much me gearing up to go out in the cold: