Because they're safety trained. The same people responsible for protecting me and my family.

If he is not to charged with felonious assault he should be relegated to working dispatch with no weapon.

These 4 rules are in line with how I was trained in gun safety. The 1st was always interpreted that if you took a gun apart for cleaning or repair, when the last part snapped in the piece was now loaded, even though you know it is not.
Never point a weapon at anything or anyone you don't intend to shoot.
Keep your finger off the trigger- absolutely.
The 4th a lot of hunters don't follow- don't "sound shoot" at rustlings in the bushes.

https://thefiringline.com/Misc/safetyrules.html
Jeff Cooper's Rules of Gun Safety

RULE I: ALL GUNS ARE ALWAYS LOADED

RULE II: NEVER LET THE MUZZLE COVER ANYTHING YOU ARE NOT WILLING TO DESTROY

RULE III: KEEP YOUR FINGER OFF THE TRIGGER UNTIL YOUR SIGHTS ARE ON THE TARGET

RULE IV: BE SURE OF YOUR TARGET

http://www.mass.gov/eea/agencies/dfg/dfw/hunting-fishing-wildlife-watching/rules-of-firearm-safety.html
Basic Rules of Firearm Safety

1. Treat every firearm as if it were loaded.
2. Keep the muzzle pointed in a safe direction. Keep the action open and unloaded. Keep the safety “on” and your finger off the trigger.
3. Be sure the barrel of the firearm is clear of obstructions. Check the chamber and magazine every time you pick it up. Only carry and use ammunition appropriate for your firearm.
4. Never point a firearm at anything you do not intend to shoot. Agree to safe fields of fire for yourself and hunting companions and never swing beyond your area.
5. Positively identify your target and what lies beyond. Make sure there is an adequate backstop when hunting or target practicing
6. Unload your firearm when climbing a tree, crossing a fence, jumping a ditch or traversing slippery or steep terrain. Never pull a firearm toward you by the muzzle.
7. Be aware of the potential for ricochet. Never shoot at a hard, flat surface or water.
8. Unload firearms when not in use, leaving the action open. Transport and carry firearms unloaded and cased when traveling to and from the field or target practice
9. Store firearms and ammunition separately in locked compartments and beyond the reach of children.
10 . Never use alcohol or drugs that can impair your judgment before or while shooting

http://www.nssf.org/safety/basics/
Firearms Safety -- 10 Rules of Safe Gun Handling

1. Always Keep The Muzzle Pointed In A Safe Direction
2. Firearms Should Be Unloaded When Not Actually In Use
3. Don't Rely On Your Gun's "Safety"
4. Be Sure Of Your Target And What's Beyond It
5. Use Correct Ammunition
6. If Your Gun Fails To Fire When The Trigger Is Pulled, Handle With Care!
7. Always Wear Eye And Ear Protection When Shooting
8. Be Sure The Barrel Is Clear Of Obstructions Before Shooting
9. Don't Alter Or Modify Your Gun, And Have Guns Serviced Regularly
10. Learn The Mechanical And Handling Characteristics Of The Firearm You Are Using

Maybe the department was too cheap to buy some?

This cop should have his badge taken away, should NEVER be in a position of authority again, and should find a job in a different field. He is not a good cop, and will never be a good cop. His actions were not only unsafe, they were disrespectful and demeaning to a fellow officer. Even if the other officer is a recruit, he is a cop. Someday you may have to trust him to back you up, or to back a different cop up. You must treat your fellow officers with the same respect that you expect and receive. If a civilian were to pull such a stupid stunt they should have the firearm confiscated and their firearm rights restricted for long enough to learn safe firearms handling.

This fucking idiot shouldn't be a cop at all, he should have been terminated on the spot, it's bad enough that the put a gun to the head of that recruit, but then he PULLED THE FUCKING TRIGGER!!!!

Even I knew at the age of 7 to NEVER POINT A FIREARM AT ANYONE AND ALWAYS TREAT THE FIREARM AS LOADED.

would be the most likely result of someone doing that in my department. Wow.