Privacy

What are the intimacy boundries in public? I just watched a girl pick ear wax out of her BF's ear while waiting on the subway platform for a train. I was reminded of the manner signs that say, "Do it at home!" I dont know how many times I've seen things like this in Japan, the reciprical zit picking is just as bad. The same couple might not even hold hands, or steal a quick kiss, but ゛Let me get that zit.", or, "What's that in your ear?" is just fine. Go figure.