In the military I worked secure communications repair. My first tour was with 25th Infantry Division. Since 25th had three Brigades at the time, and one of my unit's companies (Bravo, Charlie, or Delta) would support each Brigade. Since my shop, EMS (Electronics Maintenance Shop), was in HHC (Headquarters Company) we would go out EVERY MONTH with one of our sister companies to support the Brigade that was conducting exercises that month. We literally spent more time in the field than the actual infantry guys.
This gave us lots of training, and we were GOOD at what we did. When we would get a trouble call for a communications link being down, we'd take care of it and get back to our tent because well...dominoes, spades, PS1, and coffee were there.
But still, we'd get bored. One of the things we'd do when bored is take the heater packets from our MREs, crush them up, dump them in a plastic water/Coke bottle, cap it, shake it, and wait for pressure to build before it popped.
We had done this so much we knew the weak points of different bottle designs and would use 100 mph tape (duct tape) to re-enforce the weak areas. We'd also wrap the bottles which gave us longer "fuse" before the pressure blew the bottle open.
So, on a training exercise, bored, and it's dark. I decided to make a MRE grenade and drop it in the port-a-potty to hear what kind of noise it would make.
So I prep my bottle, wrap it in several layers, re-enforce weak areas, and rip off some strips to tap over the cap once it's on. With everything prepped I went to the port-a-potty, used it, and before I left I poured some water in the bottle, capped it, taped it, shook it, dropped in the soupy mess, and made my way out.
Then...Oh shit.
I saw the unmistakable rank of Captain. His damned chrome rank (in the field - at night) shining in the moonlight.
I saluted, "Good evening, Sir."
He returned the salute and replied, then went into the port-a-potty.
I took a few long strides to get some distance then broke out into a full fucking sprint back to our tent. I got inside and everyone is asking WTH is wrong with me. I told them to just listen...
BOOOM! "AWWWW WHAT THE FUCK?!"
So that was the last time I dropped a MRE grenade in a port-a-potty.