From there I learned that derp is basically a retarded version of "duh!" That's fine and dandy, but I also learned that it was made popular by the "South Park" guys. Now I don't want to be so hip and savy.
Funny story... for my sister's sixteenth birthday (or somewhere around that age) she wanted to send out invitations that said, "You are invited to a dope party!" This was, oh, I don't know, late 80s, early 90s, maybe, right around the height of the New Kids on the Block era, and "dope" was become a popular replacement for "cool" with them high school kids and their ilk.
As someone fresh out of tech-school and working nights, I had no clue what was going on in the world of Slang and Lingo, but I definitely knew that those invites were not getting by the goalies known as our parents. They may have been clean-cut versions of Children of the Sixties, but they weren't going to let anyone think they were make a Mary's Special Birthday Cake for their daughter's birthday party.
"Dope" did not make it onto the final draft of the invitations. At least not on the invitations we saw.