I spoke too an old school instructor and he told me of a time when instructors did yell at the students, something too the effect of "IF YOU DO NOT DO THIS YOU WILL DIE!", with the Sheriff's dive team I am on we do harassment/stress drills, shut off air,rip off masks and more but, I'am sure PADI would promptly request my OWSI if I even tried too pull any of that with students even though I do not think some challenge is a good thing, probaly why I like too teach my Rescue diver class.....