robroy:
My first artic job, 1979, 21 yrs old I done similar.
I had parked with the unit at an angle to the trailer, got out and (cringing here as I am typing) pulled the pin first.
I was presented with a trailer with 20 tonne of steel coming off the pin towards me, luckily I was young and fit and did a dive worthy of Arjen Robben to avoid the [zb] thing. 
Got a very severe bollocking and NEVER done it again, also nothing was said about the crane they had to hire to lift the thing back up and seperate it from the…damaged
unit.
He was obviously a good boss, and must have seen some potential in me as I kept my job, never forgot the guy for that and I tried my best never to let him down, but my confidence went to rock bottom being a young newbie.
Me too, 1989 imprinted on the brain “you bloody idiot”
Not quite as dramatic as You Robroy. Took a spud bulker to a remote farm in Norfolk, all I had to do was drop it, and hook up the loaded bulker. Jumps out of the cab with youthful exuberance pulled the pin, at that point the bulker started to slide of the 5th wheel, and down the lead up ramps, as cab was open, I jammed my fist onto the brake pedal, stopped like that for what seemed like an age, then thought I’d better see what happens when I lifted my hand, as I did, the trailer started to roll again, so back down with the hand, and I was wondering how long before someone might happen to pass through the farm yard. In the end after what seemed like hours, but was only about 10 minutes start to fininsh, I decided, I would have to let the trailer go, and sacrifice the lines, after all it was empty, so I lifted my hand off the brake pedal, and luckily this time, the trailer had settled in the dirt, and didn’t move, I was literally one leap onto the catwalk and red line off. After that little life lesson, I’m allways careful, about my coupling/uncoupling routine 