Hoist by His Own Petard/Theatre

The Trope Namer is Hamlet, in which King Claudius' plan to poison Hamlet ends with being poisoned himself.
- And the line itself refers to his forging a royal execution order for Rosencrantz and Guildenstern, when they were taking him to be executed.
In Oklahoma!, Jud Fry dies when he tries to stab Curly with a knife and falls on it himself.
Stand-up comedian & ventriloquist Jeff Dunham's wife had the idea to breed their pet Chihuahua, resulting in the runt of the litter, Rusty, who Jeff claims will urinate on his wife in the middle of the night when the two have an unresolved argument.
- One of Jeff's puppets, Achmed the Dead Terrorist, was killed when his incompetency at suicide bombing resulted in Achmed being the only victim of his own bomb.
In Punch and Judy, a traditional part of the story sees Punch about to be hanged for his many crimes, but he can't understand what to do with the noose... so the Hangman puts it around his own neck to show the condemned man what's supposed to happen, whereupon Punch pulls the lever.