Very sad story. Depending on the retarded man’s mental capacity, how would one explain to him “why?” Why did he get hurt for simply being friendly and telling someone he liked his shirt? Should a parent or close friend tell him to stop socializing with people completely unless he knew them very well? At our local grocery stores, we have Down Syndrome adults who bag groceries or pack the cars. They are very social and so happy to help someone. It infuriates me to think some jerk hurt a person based on a birth defect.
Even kids have to have the concept of evil explained to them at some point.