I wonder if this is how it went down...
Students arrive, pissed, and set off the fire alarm for a laugh.
Building is evacuated.
Fire crew arrives
Fire crew checks building and finds no fire
Fire crew realises someone is taking the piss.
Fire crew leaves people in the cold, in the hope students might take risking other people's lives more seriously.
Students whine about being left in the cold and wet for a couple of hours.
"We got back in at three o'clock in the morning with no explanation."
How about asking your pissed mates which one of them found it funny to set the alarm off then?