When stuff like this happens, it usually takes me a couple of seconds while I sort of digest the "did that really just happen" thoughts. By the time I have digested that "yeah, that really just happened", the moment passed. That said, if the lady did fall or I saw it again, I would say something. If the parent took it the wrong way, whatever. Allowing the kid to get away with bad behavior only encourages it in the future. Would the parent react and defend the kid? Whatever. At least the kid will know what someone noticed and hopefully they would get an idea that that action wasn't right.
I was just talking about the "punk kid" thing the other day with a teacher friend. She teaches 5th grade (at least I think) and I joking told her to remind her kids to not be punks. What spurred that on was earlier in the day, as I was walking across a cross walk on Kahuhipa St, one of the many "punk kids" I've noticed lately in that area sped through the crosswalk, just behind me. Enough to make me turn and see the car pass within feet of me. Probably 18-20 year old kid with their loud exhaust trucks and tats all over. I told that story just to vent, but she and another Kaneohe resident sort of jumped in and were like, "yeah, it's really bad here now". Then discussion went to how kids aren't disciplined these days like how we were when we were younger.