Yeah, it's annoying, some uses of the term are so good natured you really could replace "derpy" with a non-ableist term like "adorkable" etc and keep the meaning exactly the same...but a lot of others uses of it aren't. In some ways (for me at least) this is worse, at least with an unambiguous slur you don't spend a while wondering if you should give the person the benefit of the doubt before realising that, no, they really did mean it the bad way.