When I was working on a gun counter, I had an employee who was showing off. We had a rule that only managers could take down guns any further than a basic field strip, but this tool bag thought he was exempt from that. I can't remember what gun it was... I want to say it was a super vinci or something along those lines... some fairly fancy shotgun anyway. I have no idea what he did but it resulted in some spring going "Poing" and the magazine tube cap bouncing off the customer's face. The employee was so startled he dropped the rest of the gun on the floor and pieces sort of exploded off. Something went missing... I pored over the thing and never could figure out what it was but the dumb thing never did fit together right after that... had to send it back to the mfg. Most embarrassing.
A few days later, same idiot taking down a different gun. This time is was a glock. Yes, a freaking GLOCK. Not rocket science. Pushed down the tabs, pulled the trigger, and shot the slide over the counter to bounce along the concrete floor on the other side. Never did find the recoil spring.
As for me, I battled my MKII on many occasions before I finally won. Frankly, I'm surprised I never lost an eye along with all those little freaking parts. Also, tried to "help" my brother take down a crappy old rusty R1 he had picked up for more cents than sense and made an @$$ of myself when it kind of exploded everywhere and I couldn't figure out where everything went. That was back in my troubled youth though, I like to tell myself I wouldn't do that again... until next time.