While I can’t find much indication it was used before South Park, I am finding a shit ton of usages of it afterwards that are ableist as shit.
A lot of references to downs syndrome and other disabilities using visual attacks. Eyes pointing in different directions, etc.
This sort of usage has become commonplace and I would argue, makes the word weaponized no matter what its roots are.
Which means Derp is problematic.
So sorry all, I’ve been contributing to ableism by using it.