Boy, was I wrong about this one. Wrong, wrong, wrong.

Apparently, "petard" is not a kind of leotard. And to "hoist by one's own petard" is not to be given some sort of atomic wedgie.

Nope.

In fact, according to the American Heritage Dictionary:

pe-tard n.
1. A small bell-shaped bomb used to breach a gate or wall.
2. A loud firecracker.

And according to Random House:

4. hoist by or with one's own petard, hurt, ruined, or destroyed by the very device or plot one had intended for another.

Well, now I know! You may all carry on with the rest of your day.