This maybe a case of me needing to keep my big mouth shut 
Was at the park today with my two DS and friends and all playing on the climbing frame/slide. My younger DS who is 1 had just come down on his front and in the process of moving out of the way. Another little boy comes down right behind him (it's a very wide and quite steep slide) so I grabbed DS and said to other boy 'oops be careful darling'.
His mum is not impressed obviously and says to me 'he's only 2 and he doesn't understand'. No problem. But then (this is what annoyed me) cue sarcastic comments to her friend about me and my other son (who has autism) who takes a while to get on and get down the slide.
And to me, if my son was going down so close behind another child, I would explain to him why this isn't a good idea.