I have lots of examples of stupidity.
Have to say first, DS2 (12.6) has ADHD, ODD, social and communication issues, I am currently trying to get someone to look at AS. DS3 (5.7) ASD, SLD he has a development level of 2.6 yrs.
Just before Christmas I got a letter from ds2's Maths teacher telling me he had put ds on report, it said ds must meet 2 targets in order to come off report, his 2 targets where, 1, to sit still and pay attention in class at all times
2, not to talk in class and is not to call out an answer in class. When I called to tell him that if this letter was correct then ds would be on report until left school his reply was 'well surely when he takes his tablets then he is back to normal!' Like he just woke up one day and had ADHD and his meds are miracle pills.
Last year DH took dds2 to sign up for this years football season at a club he has been going to since he was in reception, he handed his forms into the woman in the club house who read over them, she looked at dh and said 'ADHD, is that what cows have?' 
My mum is the best, or worst depending on how you look at it. A few things she has said are;
'If you don't buy it he can't have it and he WILL eat what you give him. If he starts crying you will just have to tell it's tough you can't have it, he will understand if you just tell him straight' regards ds's restricted diet, at the time ds was none verbal, violent and had no understanding!
'Well he is always as good as gold for me, you just need to be more strict with him' re ds2 and his adhd!
DS1 has AS, mums words of wisdom where 'If you tidy he bedroom everyday for him he wont have a problem'
Of course, why didn't I think of that!
and for her finale when out shopping, I was looking at clothes for ds to see if I could find any nice jeans to fit over his nappy. She turned to me and said 'make sure you get something smart, you must make sure he looks nice now he is getting older. He wont look as odd then!'
I promptly picked up a top with animal from the muppets on and walked to the till.
She is lovely with the boys but she is totally clueless.