Do you do this? I have a very high tolerance, but when I'm watching a performance and my seat is literally being kicked (very hard, not taps) for half the performance, it gets annoying. Yet when the mother is sitting right next to the child and doesn't say anything, I feel like it would be rude to turn around and say "hey, can you please not kick my seat?" Especially since the child was very young and might have needed more than a request from a stranger.
When in social gatherings, I don't mind telling other people's kids certain limits I have. but these are kids I know.
Another example... we went to the museum and there were kids playing tag, no parents around, and they kept bumping into us. OR later on, my child was waiting to try an exhibit for a very long time while one child just sat there poking at buttons and the mom sat right next to her ignoring. I guess I would have said "oh, honey, there are other people waiting to try this out. how about you try one more time and then give them a turn."
So do you say something even when the parent is sitting right there? Or say something to the parent? Or ignore?
And to clarify, when I say "discipline" I'm not talking time-outs or anything like that. I'm talking about verbal requests/explanations.