When something doesn't really work in your favor, but also sort of works against your enemy.
We had to go over to that dickhead John's house. Sean accidentally shit himself, but he was sitting on John's couch when it happened. Classic double-edged butter knife.
the proverbial "Catch-22" where one is damned if one does, and one is damned if one doesn't.
"Corporate lay-offs are a double-edged sword. The company saves money by not having as many salaried people on board, but has to pay more overtime wages to the fewer people that are left so the work can be done by deadline."
Proverb used to convince one of not using a weapon (literal or figuritive) because it may come back and hurt yourself. Rather useless especially with the fact that one can learn how to use a double edge sword (literal or figuritive) effectively.
George: single edge sword is better to use cuz it wont cut you
Bob: A skilled swordsman can use any sword.
Jill: Anger is a double edge sword, it hurts you as well.
Jack: I've been using anger for 8 years and I haven't changed a bit.
Well pre-dating the Blue Steel look of Zoolander fame, this phrase refers to something entirely unrelated: a song of such depressing mood and portent that it could, figuratively speaking, drive you to put a double-edge blue steel razor blade to a very unhealthy use.
God, I am so depressed by this break-up, I just sat at home last night listening to Double-Edge Blue Steel songs.
a double edge sword is simply sword with two sharp sides, often it was used on broad swords, it is often believed of by people that broad swords are these long, straight swords, that look something like this
______
==|------->
¯¯¯¯¯¯
but that actually qualifies as a double edge sword