Are some rapists mentally retarded?

I know someone who I am starting to question their cognitive abilities. They dont get obvious ques that people are not interested. Like they will touch someone and grab their boob and the person will move their hand or move to a different spot in the room. I kind of wonder if this is often how rape happens. At this point I think hes going to rape someone and be like "But I thought she wanted my dick in her your honor". As he goes up and attempts to defend himself. I kind of think it would take a hammer to his skull to get anything through.