A person who has a lifestyle that limits their success in the world, and causes them to risk elimination from the gene pool.
The term refers to the giant panda which only eats bamboo, a food that offers little nutritional value and only allows mother pandas to raise one cub at a time. In addition, panda bears are known for being reluctant to reproduce, severely limiting their species's success.
Humans can be referred to as "pandas" when they choose a lifestyle that limits their ability to earn a living, maintain their health, or provide for a family. This term is especially appropriate when a person squanders opportunities available to them.
Examples include: vegans, who prioritize the health and well-being of other animals above their own; and college dropouts, who had an opportunity to improve their life through education but failed to seize it.
Q: Is Darren sick? He looks so pale and thin.
A: No, he decided to become a vegan. He is such a panda.