So here's my embarrasing bike mechanic confession; was a long time ago but I still remember this and say, "Doh." The freewheel had to come off a record hub so I cleverly put the notched freewheel tool underneath the quick release to hold it in place while I did the initial loosening with a 12" wrench. Freewheel broke free and I continued to turn the wrench, removing the freewheel, but I couldn't understand why the freewheel seemed to get harder and harder to turn. Suddenly there was a bang like a gunshot, and the quick release nut buried itself in the plaster across the room in my student apartment. It then occurred to me that I hadn't removed the quick release before the freewheel(!). Back in those days though, it only meant I went down to my buddies at the shop and spent $11 on another rear quick relsease. Also meant answering a couple "what the #$%$% was that?!" kind of questions, and a bit of wall repair to make sure I got my deposit back.
Little Rock Canyon, Utah