Always, ALWAYS, check who you are about to sit next to on the tube. Yesterday after work I stumbled into a seat and realised I was sat next to one the senior directors from work.
I didn't want to sit there, he didn't want me to sit there, and we both knew that neither of us wanted to talk to each other - but obviously we had to.
What followed was 15 minutes of painful small talk; I learnt that he hopes the heatwave lasts and he doesn't have a holiday booked til september, he learnt that I have a law degree and can't afford any holidays.
I hope that you learn from my mistakes and that your life is better as a result.