In the context of the doujinshi community, a subset of the anime & manga community, Sad Panda refers to a certain hidden section of the site e-hentai.org. E-hentai provides a variety of services, most importantly is its gallery, holding gigantic collections of Japanese doujinshi, Western fanfic, image collections, etc. While e-hentai hosts a public gallery where everyone can view content, it also has a parallel gallery that is exclusive to registered members. This parallel gallery is dubbed Sad Panda, because if one tries to access the site without proper credentials, the image of a sad panda is displayed. The reason people use such indirect reference to the site is because (in case word hentai haven't spelt it out) most content on the site is NSFW and many FB groups or public forums ban links to NSFW sites. People can share NSFW links by giving the gallery ID and mentioning the source is sad panda, although the latter is often omitted because the gallery ID's format is easy to spot.
Check out this doujinshi from sad panda g/924396/79fb3239de/

Source: g/921623/b574d1fc0b/
by Cercospora52C April 22, 2016
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An unhappy, disappointed person. The phrase can be traced back to an episode of the cartoon South Park, in which the "Sexual Harassment Panda" teaches the children what is and isn't sexual harassment.

For extra sadness, the "a" in sad is drawn out.
I'm a saaaad panda, because my favorite band just broke up.
by Stephanie M. December 19, 2003
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The saddest of all animals is the panda. He has no friends, no family, and no future. Therefore, a sad panda is the saddest of the sad. This term is used as an adjective or exclamation to describe moments of sadness beyond sadness but the utter depths of existential angst and isolation.
Sister: "My dog just got hit by a car..."
Brother: "That's so sad panda."

Friend: "I just failed my Geometry final and I studied so hard, too."
You: "Sad panda..."

by SKL March 11, 2008
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Sexual fetish act in which a man punches his partner to give her two black eyes and then ejaculates on the middle of her face. When paired with the anticipated look of disgust, anger, and sadness on her face, she will appear to be a sad panda.
Laura: "I'm thinking of going as a sad panda for Halloween."
Ryan: "I'll come over and help you put your costume on!"
by smiller911 January 10, 2008
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During my vacation in China, I saw many sad pandas when all the rice was gone.
by biden is gay July 27, 2019
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A mysterious person dressed in a detailed panda costume who frequently hangs out at Bowling Green in NY. He is also known to travel throughout the subways and was also spotted in Times Square.

Because his head is usually hung low, he is called "Sad Panda" by many.

whoisthepanda.com
Guy 1: "The Sad Panda is hanging near the Charging Bull again. Tourists are taking pictures with him."

Guy 2: "That panda looks so depressed. What's his deal?"
by whoishe? May 31, 2009
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A ugly Asian girl.
It is to be called out when you see a ugly asian girl.
(as an ugly asian woman walks by) SAD PANDA :(!!!!
by Glenn Eason October 24, 2006
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