Too bad it didn't "detonate" in an enclosed space, such as a port-a-potty.
Seriously, if the deployment of one of these units cause panic that results in injury or death (a stampede, heart attack, et al), the bastard wearing it should be hit with a multitude of serious criminal and civil charges. Hell, just wearing a device essentially designed to simulate the panic and terror associated with a terrorist bombing among an unsuspecting public should itself be considered a crime.
Though in poor taste, I wouldn't take nearly as much offense if war-protesters were to mark a spot in their city where these terrorist bombs would have been if Boston were Baghdad by dumping a backpack full of rose petals at the location. Instead, they want to simulate a bombing... in public... by use of panic and terror.
If the intent is to cause "terror", even if the intended/desired result is to harmlessly force the population to realized the suffering of others... shouldn't anyone wearing such a device be considered a "terrorist"?
I certainly hope no one else picks up on such a stupid idea, deciding to don a "Cherry Blossom" backpack.