On the train: entering Germany from the Netherlands, so trip was entirely within Schengen (and in fact Germany had been my point of entry on that trip for the Schengen area; I was returning to Germany after traveling around France, Belgium and the Netherlands a bit). Train stopped at German border, German train crew came on board, and an officer wearing a jacket labeled POLIZEI required me to show my passport and asked some immigration-type questions ("how long are you staying in Germany", etc.). Other passengers in the compartment were also required to show identification. A companion in a different part of the train said she was also required to show her passport and answer questions.

This occurred on 21 July 2014, aboard IC 147, Amsterdam Centraal - Berlin Hbf.

At this point I am simply more amused by the number of people who've insisted that what happened, doesn't and can't happen, than I am annoyed by it.