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1.
To be foiled by your own advantage(i.e., explosives prematurely explode).

The history of the phrase comes from the uses of a petard in a seige (a petard is a volitile early explosive capable of bringing down castle walls). To be hoisted is to be lifted or sent up, which is generally what would happen to you if you were near a petard when it goes off (and that's if you got off lucky).

The term, "Hoisted on my own petard" is incorrect (unless of course you were pulled up while on a petard, but that'd be clinicly stupid) in that the meaning is altered. This bastardization is built upon the assumtion that a petard is a spear.
Sergeant- "Did you plant all the claymores Corporal Johnson?"
Corporal- "Yes sir."
Sergeant- "Where did you plant them."
Corporal- *Looks around shiftily* "Ummmm..."
Sergeant- "You don't know do you?"
Corporal- "No."
Sergeant- "Hoisted by my own petard."

Synonym- see clusterfuck
by ArKainicW July 07, 2010