I got into it in the lobby of the Dolphin a few years ago with a mom because I "touched" her child for no reason. (What I actually did was put my hand on his shoulder to get his attention, but I'll explain.)
DH had business at the desk, and I was sitting on one of the banquettes waiting for him; the line was quite long. A group of 2-3 families were meeting up nearby before going to a restaurant. The parents had drinks and were having a lovely time chatting, but their children were bored, and it wasn't long before the kids started getting antsy and acting up. For one boy of around 6, this took the form of leaping down the row of banquettes from one to another. (These are curved banquettes, the sort that sometimes have a potted plant in the center.)
So, little boy jumps from one banquette to another, loses his balance and lands face down on the cushion, with his foot flying over the top of the banquette and hitting me in the back of the neck. His mother is laughing and sipping her drink, ignoring the child. The first time it happens, I wince and grit my teeth. The second time, I tell him to stop. The third time, I get to my feet, put my hand on the boy's shoulder, and tell him, "This is not a jungle gym. You need to stop jumping on the furniture right now." At that point, the mom FINALLY decides to notice her child, and rounds on me for daring to touch him. I pointed out that I was tired of being kicked in the head, and that I would not have had to touch him if she had been minding him. I was not about to apologize, seeing as how she thought that kind of behavior in a hotel lobby was perfectly fine.