1. offensive slang Having an intellectual disability of some kind (formerly called mental retardation). A: "Are you still in touch with that retarded friend of yours?" B: "Her name is Janet, and she has Down syndrome. Why do you always have to be such an asshole?"

2. offensive slang By extension, stupid, foolish, or dimwitted. Bill, you left the gas running again! How can you be so retarded? I can't believe I forgot to pick up milk. I'm so retarded sometimes!