I have got a ton of funny "I thought it was a good idea" stories...
I was sitting in a church revival service one night, listening to a really good, respectable, intelligent guest preacher. That night, he suddenly pulled out a bow and some arrows for his sermon illustration. He called for a volunteer from the crowd, and a guy I knew raised his hand and scrambled up to the platform. This volunteer guy was a nice guy, but he wasn't exactly the sharpest broadhead in the quiver, if you know what I mean.
Anyway, the preacher handed him the bow and the arrows, and then turned away from him and started explaining his object lesson to the crowd. Meanwhile, the volunteer was trying to put an arrow on the bow... backwards. The preacher heard some snickers, and turned and looked at the guy. He stopped in mid-sentence and said, "No, son, you put them on THIS way..." The preacher then turned back to the crowd and started talking again.
Corrected, the volunteer nocked an arrow on the string. Then he turned toward the audience and started to draw the bow... with the arrow pointed right into the crowd. (It was a big auditorium, for about 5,000 people, and there were probably 1,000 in attendance.) The preacher, upon sensing the sudden uneasiness of the crowd, turned to the volunteer, saw what he was doing, and shouted, "NO, DON'T DO THAT!" It shocked the volunteer, who had the bow drawn back about 1/3 of the way. He suddenly released the string and that arrow went sailing through the air. It wasn't going very fast, but people were jumping and ducking. The arrow arched about 20 feet into the air, then came down about 20 rows back, hitting an unoccupied seat.
The preacher was MORTIFIED, he had turned instantly pale when he saw the arrow fly. After it hit, he said, "GO SIT DOWN!" and took the bow and other arrows away from the guy. I had the opportunity to sit at a luncheon next to that preacher about 20 years later. It was strange, though... when I brought up the subject of that long-ago revival service, he clearly wanted to talk about something else. Anything else.