Hip checks on the subway

I catch the 'el' (which, on my particular line, is elevated only over a small portion of its run) fairly near O'Hare Airport; the trains are usually pretty empty when they pull into my station and I can almost always get a window seat.

That means, as the train fills up, someone must choose to sit next to me.

This frequently results in a territorial struggle.

Now, granted, I am not a small person. I do not spill over, however, into the adjoining seat; I fit within, if snugly so, the 'footprint' of the contoured seat. Except it's not a 'footprint,' of course; it's a 'buttprint,' I suppose, if it's anything -- but that sounds rude.

Anyway, when someone sits next to me on the train, he or she almost always hip checks me: We sit cheek to cheek, as it were.

When the new arrival is a large person, man or woman, such intimacy is understandable... and, of course, unintended. And when the new arrival is a comely young lady, the contact, I will concede, is not entirely unwelcome.

But it always happens: Old or young, large or small, each new arrival shoves me into the wall. I scrunch up and over, thinking thin thoughts, and often reestablish a millimeter or two of personal space -- but a significant percentage of new occupants insist on continuing to press. Why is this?