A dissappearing panda is when your having sex with a girl and right after you cum you say "look a panda" and point in a different direction, quickly pull out, take off the condom and slap her in the face with it
A combination of disappointing and depressing. When you can't decide quite how bad something is, if it's depressing or just disappointing, call it both... disapressing.
When you get so repulsed by someone or something that your penis gets forced up and out of your groin so as to displace itself at least 400 miles away; as if it were a wizard from Harry Potter apparating.
Harry Potter: Last night was awful, Ron.
Ronald Weasley: Why? What happened?
Harry Potter: Moaning Myrtle showed up while I was in the restroom, and I got a serious case of the dissapering wizard.