I posted earlier on this thread, but as there seems to be quite a lot of opinion on this subject, I won't make you go back over the pages to find my last post, so will just reiterate my situation......
....my DS1 is 5.8 and ASD. I am of the opinion that if he does something wrong whilst in public which I may miss, then another parent/adult is quite within their rights to kindly ask him to stop.
As others have said, every child on the spectrum is different. Perhaps I am one of the lucky ones as my son is impeccably behaved 99% of the time when we are out (the same can't be said of his behaviour at home/school!!). TBH I am probably one of the ones having to ask other peoples kids to bugger off behave because they have pushed or shoved my son as he is so placid around other children.
My son responds much better to someone else "telling him off" than myself or DH. If I asked him not to do something in public, he is likely to scream in my face, however if someone else asks him, he will usually do as he's told (as long as he understands what they are asking of him).
I am happy for someone to kindly point out to DS that his behaviour is not acceptable, but have been known to snottily point out my sons problems when a completely ignorant/intolerant person makes a comment.
An example of this was a few months ago in a busy Asda store. DH and I were there with both kids (DS2 was only a couple of months old). We were using the self service checkouts and there was a elderly gentleman on the checkout behind us. We were busy scanning & packing our shopping as well as trying to soothe a hungry baby when I heard a member of staff say to DS1 "Sorry, but you can't sit there". I turned round to see DS1 leaning against the conveyor belt of the checkout behind. I quickly apologised and asked DS1 to move away (which he did). No problem with that as the member of staff asked him nicely. I carried on packing my shopping.
2 minutes later, the elderly guy states to me rather loudly and aggressively "Get him to move, he's messing up my things" (DS1 was not touching anything of his, was merely resting against the conveyor belt again which was preventing it from moving properly). This, of course, got my back up & I took my sons hand, turned to the guy & said "He's Autistic, he doesn't understand, ask him nicely and he might".
The guy looked very sheepish & muttered something under his breath. I left DH to finish packing the shopping & left the store with both kids.
The point I am trying to make is that as long as someone just points out to a child (ANY child) that their behaviour is not acceptable, without shouting at them this is fine by me, and therefore the OP was not BU.
The posters who have said that it could do more harm than good etc, I can see your point, but would you not think twice about asking another child not to frighten yours if they shouted at your DC with ASD ?????