I must confess that as a teenager I used to put my feet on the opposite seats. One day a middle-aged man boarded the bus and sat down next to the seat where my feet were sitting. A while later he grabbed me by the ankles and shoved my feet off onto the floor. These days I would have the confidence to give the moron a severe tongue-lashing, but at the time I was stunned in disbelief. The man was actually shaking slightly with rage. By the time my stop came, he'd calmed down, and timidly apologised for touching me before I got off. "I should think so, too", said I. He'd obviously had a bad morning and chose to take it out on my feet.
I stopped resting my feet on the seats a few years later. As you get older, you begin to question things you've been doing for a long time and realise how stupid some of the things were. That was one of them.
You couldn't do it now even if you wanted to, because the new bus seats all face the front:
(Except the folding ones, obviously.)
] )