Given that the exact same question is the current top post but for driving instead of transit, I feel this question was needed.
My answer: I saw some guys hooking up a Raclette Grill to the outlet in an otherwise empty German intercity rail waggon. They had it unpacked in one of these 4 person seats with a small table. No idea if that could work or if draws too much power from the board net. I just headed on to the next waggon.
Guy sets a bluetooth speaker down on a seat, and then proceeds to do a full gymnastic dance routine right there in the subway car. Plenty of “regular” dancing, but also handstands, hanging from the rails, spinning on the floor, walking on the walls, the works. All well-timed to the music.
Didn’t ask for money. Just got off at the next station. Dude just wanted to dance, I guess.