If a car counts, then I guess that might be it... I hit a sheep in my Honda and did like $3700 in damage to the front end (split the radiator, busted the hood, bumper, and both front fenders, etc), and also killed the sheep
But if a car doesn't count, I guess it would be when I was working at Wal-Mart seven or eight years ago... I was driving a forklift in the back room, and I was supposed to pick a pallet up from this stack of pallets. So I forget what happened, but instead of running the forks into the slots on the pallet, I ran them into the merchandise... gigantic glass pickle jars.
So I call the night crew boss and ask him what to do, and he says to just pull the forks out, and make a break for it. I pull the forks out, and the weight of the jars on top (in addition to the two pallets on top of the pickle pallet) made the entire stack collapse. So the pickle jars all fell and broke, sending pickles and pickle juice everywhere, and pallets on top were body pillows and I forget what else, but it all fell in the pickle juice and got soaked.
I figure that's only a few thousand dollars in merchandise, but I believe that's my biggest breakage.