Avoid people sitting next to you on the train.
Maintain eye contact, smile and pat the seat next to you.......

I can recommend that solution on Arriva Trains North, Northern Rail and Virgin trains too

Ah Northern Rail. How I miss the daily cattle truck commute on the Leeds-Bradford line.

Personally I'm impressed with the number of ways there are to express displeasure when you ask 'Ist hier noch frei?' (or however you spell it). There's the eye roll, the eye blink, the huff and puff, the teenage shoulder shrug, the under breath mutter, the look you up and down like you're not fit to share the same air space and my new all time favourite, the glance and ignore. SBB rules .

Why??? It's not like I'd get a contagious disease or something!?!

And that's hardly possible during rush hours..

hehe, as a regular commuter - every morning, far, far too early for poor me, I enjoy all the pleasures of a stinking and chuckling SBB train.... sigh.
I guess that makes me just one of those persons, since I've normally got all of my books, my computer, my music player and my mobile phone either falling out of my bag or not where they are supposed to be in general (well, you can't expect me to be organized at 7am...), so I normally give everyone who would like to sit next to me (on the seat upon which I placed my bag) an evil stare. I apologise to everyone who ever had to endure that... but still, it's a bit of a tradition, so I don't think I'll stop doing it