Is there a name for this specific concept? Where somebody invents something (to do them good) but then that thing turns around and backfires on them?
Devention
I want it to be called a Midgley
Frankensteinian
I call it “Pulling a Midgely”
I don’t know of a single word. How about some phrases?
Choked on your dinner. Shoot yourself in the foot. Cut off your nose to spite your face. Dig your own grave. Sign your own death warrant.