Yes it is. It would be more polite to say something to the effect of "he/she suffers from epilepsy".
Because it is exceptionally rude. It implies that nothing that that person could have to say is important to you.
No. Epilepsy has many forms and many causes. So for each person it is different. For that reason there is no one food that you could say should not be eaten by any person who has had an epileptic seizure.
It is politically correct to say that black people are african-american. And white people are just white.
To be incorrect is avoir faute
A person from Mumbai is a Mumbian. Some people incorrectly say Mumbaikar -- while this is correct in the Marathi language, it is definitely incorrect in English. Another incorrect term is Mumbaiite -- just doesn't sound right!
you cannot say "he have" this is incorrect, it is " he has"
I would say NO, but always consult your doctor... not the internet.
It is grammatically incorrect to say sister and sister. You just say sisters.
Person years. More popularly know as Man-hours or Person-hours. Recent politically-correct alternatives include Person-hours, Staff-hours and Employee-hours.
This happens some where every single year. So to say "The Last" would be substantially incorrect.
No, it is not incorrect. You could say, "These ones are the best for baking."
"Why did you say that?" is correct English. "Why you said that?" is incorrect, though people would understand what you meant--however, an educated person would not speak that way.