I would be mighty pissed off if I was sitting to children whose parents did this. My 2 DDs are 10 and 14 and very well behaved, but I would never do this. Things happen, they drop colouring pencils, they want their bags down, they want the loo, they blare their ipods, they get sore ears, they don't like the food, they act the goat.
On the way back from NY, DD2 had, unbeknow to us, contracted swine flu, and projectile vomited, in her sleep, all over me It was bad enough that I knew her, never mind a strange child doing this!