I made the mistake of dropping a Fatboy launcher in Sanctuary while I was over-encumbered and trying to do some scrapping when the Settlement came under attack.
Aaaaaaah ... no, it's fine, I've got dozens of Heavy Lasers out there, unless it's a Behemoth, we're fine.
Finally finish scrapping, look up, there's one of my Setters who has grabbed the Fatboy and is running towards the Super Mutants ... who are standing in-front of my Generators, firing impotently at them thanks to the Junk Walls I've erected around them to prevent just this kind of shenanigan.
"What is he ... no. NOOOOOOOOOOOOO!"
Fwumph-psssht! goes the launcher as the sole shell in the thing goes flying through the air, misses the Super Mutant and lobs right into the cluster of generators behind the Junk Walls.
Suddenly EVERY TURRET IN THE SETTLEMENT STOPS FIRING. But the Super Mutants are all but untouched.
It was a hell of a fight. And I was sorely tempted to shoot the Settler in their behind after that. But lesson learned, I guess.