Hourglass Coffee Mug

I have often had cups of tea/coffee made for me or by me, and more often than not, I leave it on the counter next to the kettle to 'let it cool down'. More often than not, I accidentally leave my cuppa tea (or coffee), either by my side or by the kettle, for too long and it is barely room temperature when I remember to drink it.

An easy way to solve this would be an hourglass-shaped mug, with a middling-section that expands upon exposure to heat to restrict flow (therefore the trickle that does get through is more exposed to the air and thus it cools down quicker), and as the main body of tea in the top section cools down, the expansion of the middle section will slow and then decrease, allowing more tea to flow through the bottleneck. If the measurements of the bottleneck is just right, the temperature of the tea should be hot, but not scalding hot. The expansive area should become reduced enough for drinking with ease, but not 'sculling'.

Could be adapted to a funnel-like version with a filter, so people can make freshly brewed coffee and tea in the office breakroom. Could also be adapted to mark down a few minutes if filled up with boiling water/tea/coffee to a marked line.