Why does room temperature coffee taste so bad, even to asnomics?
The initial statement is too broad. It is not true that room temperature / cold coffee tastes awful. It is highly dependent on how good the roasted coffee is. This is why coffee cuppers drink coffee at room temperature.

ANY defects in the coffee are amplified as it cools. This is why almost everyone likes hot coffee. Unless you have really good coffee, you can detect off flavors and bitterness as it cools. With really good coffee, the flavors actually improve /expand as it cools.

Source - I roast my own coffee every week on a Hottop roaster. I drink coffee black, and I can drink my coffee cold with no problem. Can't say that about Starbucks, Dunkin Donuts, etc.