When some people have just got off the tube, I have to think fast. I stand there, book in hand, taking in the situation. First, I count the number of seats that have become free, assess how far they are from where I'm standing, and if anyone is nearer. Then I look at the people who standing, and the people getting on - I scan for the tired, the pregnant, the old - to if there are any who deserve a seat more than me*. Lastly, if the second test didn't turn up any bellyswell or drooping lids, I make a decision on which seat to stick myself in. This is an involved decision, you look at the stance of those on either side, how sweaty they are, how much they're encroaching, etc. And all of this is done in about 3 seconds. It's a stressful business, commuting.
Today the girl I sat down next to made a funny little muffled noise, turned and snuggled up to me. She continued to sleep, now resting her head on my shoulder, for the rest of the journey. I wasn't quite sure what to say, waking her up would have been more than a little embarrassing for both of us and she was my age, and pretty, so I didn't really mind.
I realised as we were coming into London Bridge (my stop) that she might have missed her stop, so I did the gentlemanly thing. I stood up, stepped back, and trod on her toes. She woke up suddenly, and stared around for a moment. I said 'whoops, sorry' and got off the train. I saw her on the platform a few minutes later, so she didn't miss her stop, and was excused the embarrassment of realising that she'd curled up and gone to sleep on a creepy stranger's shoulder. It seemed like the most humane way of doing things; I didn't tread on her toes very hard.
*I'm aware that now that my knees are OK most people deserve a seat more than me, but what I mean is, 'that deserve a seat sufficiently more than me to make me give it to them'