"I heard some noise from the other room, are you okay"
"Yes, sorry, I was watching a horror movie and my popcorn got stuck in my throat, so I starting derping."
A lot of people like pugs and think they are cute because of their derpyness, but most people aren't aware of the breathing problems that pugs and other similar flat-nosed dogs suffer from as a result of negative mutations resulting from decades of selective breeding.
A verb to describe the action of somebody or something that is acting in a manor that would cause somebody to think that they are mentally handicapped.
When Iryna fell on the floor and started laughing uncontrollably for absolutely no reason, Ryan and Matt mutually agreed that she was derping out.