Sue over what? The existence of a cross eyed character on TV? The existence of a clumsy character on TV? And even if they could, this isn't about any parents.
This about people on the web redefining language to find it offensive, aka "ableism". The words these people find offensive. Stupid, idiot, moron, crazy, lame, dumb, bitching, nagging, blind to, deaf to, cretin, insane, imbecile, invalid, nuts etc. etc. . Yes, these words are just as offensive as "derp" in their minds. It's just, derp has garnered so much attention now that people have actually started taking them seriously.
If they would have put derp alongside all the other words they find offensive people would see it for what it is. Pointlessly trying to be offended by the English language on the behalf of differently-abled people. It's pretty darn offensive how they think saying someone is nuts = discrimination against differently-abled people, like if there didn't exist any real causes to help with anymore.