system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does coffee taste amazing when it's either hot or cold, but taste awful in between?
gpt
Different flavor characteristics come at different temperatures. The hot or cold tends to mask certain flavors, especially bitterness. Our taste receptors are more sensitive depending on the temperature of what we're eating or drinking. 

Once the temperature of coffee is hot or cold enough, our taste buds are less sensitive and we can't quite taste just how bitter coffee is, but once the coffee lukewarm you'll be able to taste just about everything, which you may or may not like.