I have two. Both not the worst in terms of total delay but memorable for being horribly annoying.
ICE train from Dortmund to Karlsruhe (Germany) in December 2017. We’d had a couple of centimeters of snow the night before but nothing too drastic… until right after Frankfurt am Main. A railroad switch near Frankfurt am Main Stadion was frozen and could not be operated so we had to stop for over an hour at that tiny station. In the meantime, the beer in the onboard restaurant had run out and some already drunk passengers stole the conductor’s phone to blast the anime music over the train’s speakers and argued who would leave the train to buy more booze. Eventually we had to return to the previous station where dozens of additional passengers boarded. We were confused but got told that ours was the only train that would even attempt the rest of the trip. In the end, we arrived about three hours late.
A trip by regional train from Kassel to somewhere near Duisburg (Germany) in September 2021. Should have taken about four hours but due to an unexpected storm and a tree that damaged the overhead lines, the train had to stop in the middle of nowhere. It took 90 minutes just to figure out which taxi company would take us to the next station and a total of eight hours to get to our destination because it was so late at night that at some point no connecting trains were available.
I have two. Both not the worst in terms of total delay but memorable for being horribly annoying.