Other forms: pessimists
If the world can be divided into those who see the glass half empty and those who see the glass half full, the half-empty crew are known as pessimists––they always see the worst.
The opposite of pessimist is optimist––someone who always sees thing in a positive light. Most people insist they are optimists, and when accused of pessimism suggest they're only focusing on reality. In fact, though, people who see reality as it is are called "realists."