The biggest issue I see with your usage of that mug
@Fishy is that, based on your other posts, you are apparently filling it with coffee from a Keurig, which I don't think gets the water hot enough for the extraction necessary for a great tasting cup to begin with. I'm sure it tastes better if you keep it hotter, but I think
@storrsroars 's point is that you are better off starting with a better cup of coffee from the get go, in which case it will actually taste quite fine if it cools a few degrees while you drink it.
Personally, I keep my brewed coffee in an insulated vessel until I drink it; that way it retains the heat without needing to heat it up. But if you are merely heating coffee that wasn't extracted at a high enough temperature, I agree with storrsroars that you are more likely masking the taste of a less-then-great cup to begin with.