@Wrath of Foamy
@HereticBD
To answer all of your questions, we came into the situation late, so we don't know what was said before, but it appears:
You have an 18 year old kid (most likely a high school senior) putting up her feet on a train. then the cops tells her to put her feet down, but does not explain why she should do so (based on their conversation after he yanked her off of the train, when he tells her it is against the train rules and she is surprised), he then tells her she has to get off of the train because she "disobeyed" him.
The cop came off as very unprofessional, and power tripping on a little girl (her big girl friend was waay out of line and disgusting) who was putting her feet up on a train and didn't understand that the cop was being a real stickler (the train wasn't crowded and nobody needed the seat, she wasn't homeless and trying to sleep on the bus, she wasn't dirty, etc.,) to train rules she didn't know. There is a way to handle that situation professionally, if he had explained that it was against the rules and if she didn't comply he would need to remove her from the train, then he would be in a much more defensible position, he probably wouldn't have needed to arrest her, and he probably wouldn't have needed to call in the whole precinct over a 4 foot girl with her feet up on a train.