The Meaning of Hoist with One`s Own Petard
First used by Shakespeare in Hamlet, in modern usage the phrase hoist with one's own petard means to be harmed by one's own plan to harm someone else or literally hoist, or blown upward, by one's own bomb.
With a tip of the turban 
to the blog Puppies and Flowers, there's no better example of the meaning of the phrase than in the following story from 2007:
news.com.au, 22 May 2007, Man's plot to kill girlfriend ends with his death
A CALIFORNIAN man who tried to kill his girlfriend by leaving her in a car parked across railway lines was himself killed when an oncoming train hurled the car into him as he fled.
His girlfriend survived, the Associated Press reported.
The man drove the car to the head of a line of traffic stopped at a level crossing in the San Fernando Valley neighbourhood of Sunland on Monday, police spokesman Mike Lopez said.
The man, who was seen arguing with the woman, then parked the car on the tracks and jumped out, leaving her behind, Mr Lopez said.
A 450-tonne commuter train hit the rear of the car, launching it into the man.
The girlfriend, who was injured , was taken to hospital in a stable condition.
"She gets hit by a train and lives. He gets hit by his own car and he dies,'' Mr Lopez said.
In modern English it is more likely that we would use the phrase poetic justice to describe the same result.
Wouldn't it be marvelous if the entire Muslim world received the same measure of tolerance and love that it dispenses to Christians, Jews and other infidels? Wouldn't it be poetic justice if the Muslim wish for Allah to destroy all evil in the world came true and tomorrow we would find the faithful followers of Islam all gone?
