I am coming off the husband cleaning icing chemicals thread. I know you aren't supposed to mix chemicals, but I didn't know that you could make chlorine if you mix the wrong stuff! If i had known that I wouldn't have scoffed at my mum when I was a teen while mixing bleach with every other nice smelling spray I could find.
There are others, my 3 year old for example used to try to put his hand in the lift doors of our flat. (years ago he isn't scarred for life) I used to tell him we Don't do that, it will hurt him, he will get stuck blah blah blah.
He did it one day and i thought fuck it, googled 'child's a caught In lift' and showed him a video of a little girl getting her arm stuck. Never did it again.
Can anyone think of any others?