Been thought of.
The spooks used to doctor Vietnamese ammunition and grenades which were supposed to be left in place of the real stuff when caches were found.
The ammunition was designed to destroy the breech of anything that shot it, maybe take someone's hand with it. The grenades didn't have fuses.
Sometimes it was actually left. Most of the time just thrown away rather than haul it around in case a cache was found.
Don't know if anyone actually used the stuff. Wouldn't have been around to tell anyway I guess.
Arf