The beginning of the term was always easy for the 'quick prank jobs', as students filed into the Great Hall the morning of the first day at Hogwarts. Students were groggy from lack of sleep after celebrating with their new and returning housemates, which made them perfect targets.

Peeves would be lurking around the banister overlooking the lobby. Unsuspecting firsties were the best because they didn't know him yet. So as they would teem just outside the hall, Peeves would aim his water balloons at them.

Nothing like entering the Hall for your first morning at Hogwarts being soaking wet.