People collectively who are mentally retarded.
1People who lack one are considered developmentally challenged, even disabled.
2Annika looked at him as if he were developmentally challenged, and he backed out the door.
3Do you see why I feel like I've been stranded in a life skills class for the developmentally challenged?
4I was really starting to hate the man's laughter: it made me feel like a developmentally challenged kid hamming it up in life skills class.
5Developmentally challenged, but not insane.