I'm always cocking up! Some are far too outing but one that still makes me laugh is this one,
At work one day and we were horrendously short staffed (as always) so I was running around sorting out till problems and trying to get stock out at a ridiculous pace. I was putting out a pallet of 2ltr lemonade bottles which are covered in a jacket of plastic and as I went to cut off the plastic I pierced about 5 bottles at the top of the pallet. There happened to be an elderly man walk past me right at that moment and ended up soaked from be sprayed by exploding lemonade right at head height, his face was dripping
I couldn't get the lemonade to stop either
He was ever so good about it and his wife found it hysterical but I was mortified at the time.
Whenever I think of that incident now all I can see is the little elderly chap dripping wet and being sprayed
It's surprising how far and hard fizzy drinks escape their bottles when you pierce their bottles 
Some others come to mind...
I had to stop a cashier from charging a poor lady £689 for a joint of beef (mixed up weight/price per kilo)
I've gone around far too many corners too fast with a pallet on a pump truck and it's landed on the floor, especially bread pallets as they are so light 
A young lad forgot he left a pallet of meat on the shop floor rather that put it in the fridge, all had to be wasted costing thousands
A delivery driver was in a foul mood and was rushing the drop off. He went round a corner with a pallet of alcohol too aggressively and the lot toppled. Smashed champagne, spirits, wines and bottles everywhere! He soon started trying to act nice after that as he needed help clearing up
A colleague over loaded a display table of 10ltr paint tubs so it broke and we had paint all over the warehouse floor. Same thing happened with fence paint and smaller 1ltr paint pots, we don't learn in out store it seems 
We have an electric floor cleaner which is sometimes used to clean spills. A colleague decided the floor cleaner was the best way to clean up a 1ltr bottle of washing up liquid that spilt on the floor. Yep, bubbles everywhere! The aisle had to be shut off while we cleaned up the river of bubbles 
I'm sure I'll think of others 