Easy. A Rossi M68/69? (blued snub 5-shot .38 Spl.) Think I paid ~$60 for it, back in 1982 or so. Bought at an estate sale. Figured I couldn't go too far wrong for that price. Boy, did I miss that call.
Stupid thing would fire one round, and the cylinder would come unlatched, and move outward about 1/16"...just enough that a subsequent trigger pull did nothing at all.
Slap the cylinder back into battery, it would fire one more round, and repeat the process.
I replaced the ejector rod and spring, checked the cylinder release, checked the hole in the frame where the ejector rod locked in...nothing obvious.
Wasted a lot of time/effort/ammo (since I lived in CA at the time, each new "fix" required a range trip to test).
When I ran out of ideas (I am mechanically inclined, and was an aircraft mech (A&P) at the time) I surrendered and took it to a gun shop. Not to say that this guy knew anything, but after telling him everything I had done, he told me that it would cost more to fix it than it was worth.
I took his word for it. Took it home, beat the fire out of it with a sledge hammer (great stress-relief therapy) and threw it in a lake.
End result was that it gave me a case of revolver aversion disorder that lasted about 20 years.
I finally overcame my disorder when I expressed an interest in an S&W M66 on GunBroker around 2004. Wife bought it for me for my b-day, (bless her) and the pieces fell into place. I have owned a number of S&Ws since then, and finally have an appreciation of revolvers.
Never too late for an old dog to learn new tricks....
Best regards, Rich