When a student graduates from such a demanding course, they have to be recognized in some fashion.
Here's what I suggest:
Each student is graduated individually, the students who are waiting are sequestered in another room where they cannot see or hear the festivities.
The student is invited up to the podium, and an announcement is made to the effect of
"Congratulations Diver Doug! You have mastered the skills of the Open Water Diver, You've been pushed off the side of the pool and have had your air cut off, you've had your mask ripped off your head and your regulator out of your mouth. You have survived having your leg hacked to pieces, amputated and reattached. And you've been drowned and brought back to life! Welcome to the ranks of the certified diver!"
Then as Diver Doug is presented with a glimmering necklace of mirrors and silver and glitter which is placed around his neck, behind him a panel silently opens which is covering a pool full of baraccuda and a great white shark, and the presenter says "Doug, one more thing"..and gives him a hard backwards shove.