Fortunately, I'm one of those real careful guys and haven't had any mishaps. I've only been reloading for 37 yrs. though.
One of my old friends had a bad habit of having several cans of powder on the bench at once. I told him that was a bad idea. One day he ran out of H4831 in his measure. He inadvertently grabbed a can of H4895 and finished loading his 7MM Rem Mag cases. The next day another of his friends touched one of those off at the range. It knocked him off the shooting bench, broke the wrist of the stock, blew the floorplate out of the stock, and welded the bolt shut. After pulling the bullets and discovering his mistake he found he'd loaded it 13 grains over max for H4895 powder. A gunsmith removed his bbl. and got it all apart. It didn't hurt the Remington action or bbl. but it ruined the stock and bruised the shooter's face pretty bad.
Another friend, an ex-employee of a firearms manufacturer, once thought he'd go real slow and see if he could push some live primers out and replace them with a different primer. Bad idea! It's always better to soak them to kill them or, better yet, just fire them without powder and replace them with the primer of choice. Anyway, he didn't wear eye protection, either. A primer went off. My friend now has only one eye. Never! I repeat... never try to decap live primers!!