When I buy coffee or tea, it has two temperatures: dangerously hot and, twelve minutes later, disappointingly cold.
The problem is particularly bad with takeaway cups. When the drink is still hot, sipping through the little hole in the plastic lid delivers a narrow stream of near-boiling liquid directly
onto the tongue. Actual slurping, which would mix air with the drink and cool it before it reaches your mouth, is nearly impossible through the lid.
The solution is a small plastic attachment built into the standard drinking hole of a disposable coffee-cup lid. Instead of simply allowing liquid through, it draws in outside air through a second opening and mixes it with the liquid as you drink.
At the same time, the valve restricts the flow of liquid. Instead of getting a mouthful of 190-degree coffee, you get a smaller stream vigorously mixed with room-temperature air.
The valve would only be useful while the drink was hot. Once the coffee or tea cooled to a comfortable temperature, the entire valve could be pushed sideways, leaving an ordinary unrestricted opening.
Possible luxury version: a powered air inlet, allowing the drinker to select anything from Normal Sip to Coffee Nebulizer.