Gluten free diets can make a huge difference in cases of autism (and related difficulties). To see an article on this have look at this link to the autism research unit The page aso includes a link to the ARU homepage where you can get instructions on the test (very sinple just involves collecting the first urine of the day).
Children who are helped by the diet (and those involving the removak of casein) have leaky guts, so breakdown products of gluten that would usually remain in the gut pass across the blood brain barrier and act like opiates on the brain. On removing gluten you can therefore see withdrawl behaviours- lots of tantruming, head banging, screaming etc. Most children on the diet also require the remoavl of MSG, aspartame, and thigs like gelatine (which contain the same thing as MSG). it is a very strict diet- far stricter than the coeliac diet. However if it works it is incredible. The literature says to give it a 3 month trial- in my experience if it is going to work it works dramatically in days. After removing gluten etc a close eye needs to be kept on the diet and further foods may need to be removed. An excellent organisation is "Allergy induced Autism" (AiA) - there'll be a link to them from the ARU homepage which can be accessed from the above link. Some good books are those by Marilyn LeBreton and Luke Jackson (a 13 year old on the diet). Also an american (i think) publication "special diets for special kids".
As someone else said fish oils can also be useful- especially in cases of ADHD or developmental dyspraxia- both of which can look like bad behaviour. Efalex or EyeQ are bth good brands and can be found in Boots. Slightly different formulas though so it might be worth experimenting with both.
FWIW I have some cards to hand out for people who are tut tutting at me in public, produced by BIBIC (British Institute for Brain Injured Children). They satrt "this child has autism. He?She is not being naughty and we are not being bad parents for not reprimanding them"
Obviously I have no idea about your friend, but undiagnosed AS (Asperegers) ADHD or developmental dyspraxia (all of which it wouldn't be unusual to be undiagnosed in an 8 year old) can look likebad parenting. Guess I'm just saying don't be too quick to judge. Also if there is a problem it can be very difficult to parent effectively if you don't understand why your child is behaving the way he is.