My father keeps saying that I'm mentally retarded because I'm obese?

That is WHACK!You know the my Mother's doctor accused her of having a psychiatric illness just because she told him she thought she had Lyme Disease?You are not mentally retarded and you do not have to prove ANYTHING to these people.I'm telling you I think these doctors are the retarded ones!You just live your life and keep them out of it.If you have no medical condition those false reports shouldn't give you a reason not to file a lawsuit against this person.Make sure you have people behind you on this.Otherwise the court should know there is nothing wrong with you if you express your opinion in a civilized way!Good luck!