YES!!! People are so freaking oblivious these days! They think anything even remotely child related can be treated like a McDonalds play yard.
The BEST way to address those type of things is cheerfully and RIGHT AWAY, like 3rd kick to the seat could have been, "Hey, (big smile) Believe it or not, the whole connected row of seats is jolting so can she please not kick?" Then at least if she just literally has never taught her kid how to behave in a theater, on a plane, at a restaurant, whatever, she'll KNOW people are bothered and hopefully LEAVE at intermission if she knows she has no way to stop her child from kicking. Otherwise, people just think "Everyone understands".
As for the flashing cameras, freaking INGRATES! I guess all you can do is shrug because the announcements already made it clear that it was NOT ALLOWED, but even still, if someone was right by me doing it, I'd remind them it wasn't allowed, and my husband?! He would have enjoyed confronting anyone within ten rows of himself.
There is a BIG difference between trying your best to teach your kids how to behave in a theater, and having some difficulty, and NOT EVEN TRYING and setting a bad example yourself by flashing the camera when the announcement said not to. People suck, that's all I know. They seem to righteously think it's IMPOSSIBLE to act any other way than exactly how they see fit, and to those of us not raised that way, and not raising our kids that way, it's depressing.