I have the experience of traveling by bus for more than ten years, and I saw all kinds of situations. When I saw this etiquette I thought something like this should be put in buses, trolleybuses, and in the other vehicles used for a public transportation.
Once I was in a bus with mother and sister, going to the train station. The bus was half empty, meaning there were a few empty places. We heard the voice of an upset and angry lady trying to protect her from an older man who was sitting behind her. We saw what happened. He was touching her through the opening on the seat, but when she turned around he pretended like nothing happened. She tried to change the seat but that didn't help. Many people in the bus protested against him, I thought she should slap him. Luckily he left the bus soon after.
When I am in a crowded bus I stand in the parts of bus where there are more women, or I turn my back to the bus side so I can see what is going on in front of me. 😀