Sad panda

[Becky]

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 isnt sexual harassment.
For extra sadness, the a in sad is drawn out.

[Tanya Shivari]

In the context of the doujinshi community, a subset of the anime

[Donald Trump]

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.

[Sarah]

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

[Donald Trump]

an overworked and underappreciated person, who usually wears tan-on-tan or gray-on-gray clothing, and who threatens his superiors with bodily harm and resignation on a daily basis.

[Sonia]

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.

[Justin Bieber]

A term often misused in a multitude of ways. It is not an acceptable synonym for “I’m in a sad mood”, “you’ve made me sad”, or “I’m emo now”. It should not be said in any circumstance ever. It SHOULD stay on South Park and the commercial that South Park spoofed off of. IF it is in fact used in every day conversation it should be known that it means “I can’t come up with my own jokes and I’m probably only even saying this to annoy people because in my immature state of mind I find that funny.”

[Luis Fok]

When you are receiving [oral pleasure] and the person delivering the pleasure is crying from the two [black eyes] you gave them for not [doing it right] first time.

[Gregory]

A ugly [Asian girl].
It is to be [called out] when you see a ugly [asian girl].

[Donald Trump]

A part of the phrase, Im a sad panda, to use as often as you can in every conversation ever to everyone you know.

Use it especially if you want your online [buddies] to talk about you behind your back and call you names like the following: geek, turd, jerk, [pig], fool, dick, [fuckwad].