I'm gonna name my first born son retarded so that when people ask me "Are you fucking retarded?" I can answer "No, I'm fucking my dog."
Wow, I'm not even sure what to say to that. Is that really what you're going to do?
No, it's just a joke, you dummy. Jeez, lighten up.
It is pretty inconsiderate to make fun of mentally disabled people, and to use slurs against them. Even though it's just a joke, it's still a really awful thing to say. If you want to make people laugh you should try to do it without making rude statements about others.