Space Invaders drive me mad

Why is it that though the space available in this world it is never enough for some people and they have to invade the space of others. I have now given up with public transport as I am so fed up with people sitting on my lap when they get on the bus. Usually there are 5 or 10 seats and someone will get on the bus and rather than sitting on the empty seats, they will sit next to me and catch my leg under there backside, then they will keep moving in till they are satisfied that I my head is squashed against the window and my legs are folded over one another.
This is one of many scenarios that occurs everyday in my life of public transport travel, an example of another is when I am standing at the exit door on the bus. The bus is moving packed with people crammed together and you cant move for fear of falling over and more importantly fear of falling on top of someone else, then a passenger who wants to leave the bus will come and stand right behind me and will persistently start pushing his/her body towards me to move me so they can get of at there stop which is still half a mile down the road. Is it not clear to them that you cannot get of the bus whilst it is in motion, its so frustrating and I cannot understand why this physical abuse is necessary whilst travelling to work or going shopping.

These are everyday occurrences in my life and I am starting to wonder if I am the only one with this problem, am I the only one who does mind being sat on and pushed.
I have had enough of using public transport and cannot understand why people need to get so close that they might aswell ignore your existence. I really cannot take it anyone. I do not want their bottom on my coat, stopping me from moving, I do not want my air supply cut of or contaminated by their fish supper breath. London is a busy place, but we all need some space and do not wish to be pushed, shoved and sat on and it would be really great if they could sit on the seat that’s available to them and not the seat already vacated by somebody else. I wish they would stop the ignorance and think of others.