Jam a bunch of people together in a tight space like a bus or the subway and something crazy is bound to happen. What's the most memorable thing you've seen on mass transit?
I rarely see anything "crazy".  More like subtle and beautiful.  Mass transit is not for the hurried or the bothered.My life isn't exactly mapped out to make mass transit a regular viable option.  I live in the city and work in the suburbs.  When my car was in the shop for a week, I used mass transit to get to work and back, but it wasn't easy.

I woke up at 5:00 a.m. to eat, shower, and walk about 1/4 a mile to the bus stop...a peaceful but eerie walk through the unusually empty streets in the greyish gloom of an August morning in Minneapolis.  I took the W downtown, walked three blocks north and waited for 15 minutes for the Southwest Station bus to arrive.  The W was packed full of regulars; men carrying thermos mugs and brown bag lunches having casual conversations that can only occur on buses:  "Humid enough for ya?"..."Catch summer training stats for the Vikes?"..."How has Agnes done with the latest round of chemo?".  I felt like an invader.
Waiting for the South West Station bus, every passing bus would halt at the corner in front of a man waiting for the same bus.  The doors would open with a rush of air: "Nicollet Mall"... the man would shake his head and thank the driver....the door would close and the bus would roar away.  The man was so casual about his long steel cane with the red walking tip that it astounded me any of the bus drivers had been observant enough to stop.
The ride from downtown to the Southwest Station in Eden Prairie was a two-hour ride.  The man dressed in the same polo shirt and khakis everyday napped the whole way.  My third day on this route I had to lean over and shake him awake as our bus pulled into the station.  He wiped saliva off his face with his sleeve.
My ride home was an excruciating three hours.  The day the shop finally called to say my car was finished, it seemed especially long.  Until the last downtown stop, a big rough looking man stepped on the bus with a woman and a stroller.  The man had a scorpian tattooed on his neck and the woman had caramel skin and heaps of kohl-black eye makeup.  Sitting pudgy and cherubin in the stroller was a tiny cartoonish version of they man with black curls boinging from the top of his head.  He grinned, gap-toothed at anyone who looked in his direction.  The old women that shifted nervously when his parents stepped on board, now cooed with delight at the new passenger.  His mother played peek-a-boo, coaxing squeals of delight from her son, much to the amusement of the passengers. 
What a precious day for a family ride on the bus.