I play this game twice a day. On the Philly trains, there's a 2 seat row and a 3 seat row. I always choose the 3 seat row and grab the window, thinking that the next person will sit in the aisle, and the 3rd person rarely wants to ask the aisle person to move in or get up so they can get the middle. It's a whole strategy.
Still, I end up with the fatass more times than not. Of course, most Americans are fatasses so the odds are stacked against me. The ideal seatmate is a 5 foot tall Asian woman, not because that's my type but because she's likely clean, quiet, and takes up no space.
The other day a woman in a seat in front of me had her Kindle on with the font set at about 50 and I couldn't help but see she was reading explicit erotica. It was all sorts of wrong. In case you're picturing the hot brunette from above reading the erotica, I'll not shatter that image with reality.