I love it when I fix something completely by accident.

The laundry machine at my friend's apartment building suddenly stopped working. If you put a quarter in, it ate the quarter but beeped loudly and said "error". So I went down to the laundry room with a Swiss army and a flashlight, and stuck the blade into quarter slot. I blindly jabbed at the coin return like a monkey trying to kill something with a stick, and after about four minutes of this, it released a coin jam and now the thing works perfectly.