I didn’t know that
For some reason (ok, ignorance) I thought that “to hoist by one’s petard’s” was to hang somebody with their own pants! You know, “leotards” rhymes with “petards” and I had a mental image of some medieval pants; the logic was, nobody could afford rope, so you hung them with their clothes.
Wikipedia has the definition: http://en.wikipedia.org/wiki/Petard
Talk about a kick in the pants!