Wow this is sad,
first
The word retarded is an actual medical condition that many people have around the world, along with dumb (also known as a person who is mute). It does not mean lack of intelligence.
There are many ways of belittling someone's intellect without insulting people with medical conditions.
I mean what's next saying someone has a brain tumour to indicate their lack of intelligence?
or what about fetal alcohol syndrome or even autism.
Please show respect to people and use other language.