Note: To achieve this, you'll need the PC version, and the Bully trainer, with the one-hit KO option on.
Right! So, basically, when you're in the gym, grab the fire extinguisher by the basketball court (or enter the gym with one), and then, while continuously spraying, run from the court stairs to the pool stairs. You should hear people getting knocked out behind you, and when you look back, there should be a few people on the ground squirming.
In the gym, peds only spawn in one area out of the three: B-Ball court, locker rooms, and the pool. The second you leave one of these areas, all the peds in the place you were in despawn. However, peds also don't spawn right in front of you, so I think that's why they spawn behind you in the locker rooms area.
If you have the PC version, try it out. It's hilarious hearing the random KO's.
Part two:
Using the same trainer option, go to the boy's dorm, and sprinkle marbles all over the exit area, then pull the fire alarm.
Not only will all the students trip on the marbles, but they'll also be knocked out.
