Lacking understanding. Not making sense. Nonsense.
The origin of Derp is easily found, but often wrong. Some claim it began with BASEketball, a 1998 film by the creators of South
Park... which in turn led to the replacement of
Chef by a Mr. Derp.
Close, but no cigar. The real origin predates 1998 by more than two decades... but Chef is a nice parallel with the original origin, which was surely the inspiration behind the name of his replacement.
The first appearance of the original was on The Muppet Show "Sex and Violence" which first aired in 1975.
The Chef in this
case was Swedish. He never said anything remotely English, and spoke in a strange language that was strange enough to be almost Swedish.
Quite often he said
something that often sounded
like "Herp derp herpy derpy"
That is it.
Pure and simple. Completely lacking understanding. Pöpcørn shrimpee. Herp derp.