With Minute Physics' videos we pretty much expect to have the universe explained to us in...a minute. Or maybe a few minutes. But this rundown of temperature and how to achieve "negative temperature" only takes 10 seconds. Impressive.
If we're talking about temperature measured in Kelvin (you can experience negative Fahrenheit and Celsius temperatures pretty easily) you have to redefine your quantum system so that more energy means more subatomic particle organisation, not less. This would allow you to measure negative temperature, but the energy in the system would still be positive. That's all it is. Seriously. We're done here.