Sad Panda is an internet slang used to describe someone who is sad or depressed. The phrase was originally used in the popular Comedy Central animated series South Park. Since it start on South Park it has been used in pictures, videos, and forum posts.
The phrase Sad Panda originated from the South Park episode Sexual Harassment Panda. In the episode, the kids in Mr. Garrison’s class are introduced to the Sexual Harassment Panda. After giving an example of sexual harassment to the class, Sexual Harassment Panda would then say “That makes me a saaaaaaaaad panda.”