It's about the degree of harm. Spreading glitter and fart spray in somebody's car doesn't really hurt anybody, and it's very unlikely anyone would prosecute ove

It's about the degree of harm. Spreading glitter and fart spray in somebody's car doesn't really hurt anybody, and it's very unlikely anyone would prosecute over it, no matter what the circumstances were. Breaking someone's legs is very different in the eyes of the law. Booby traps are generally illegal because they are indiscriminate. It may be justified self-defense to hurt somebody, even to a crippling or lethal level, if you knew it was necessary to save your life or prevent some other serious violent felony. Booby traps could harm anyone, regardless of their intent. If you were to set up a shotgun trap to fire on anybody who opens your door wrong, for example, it might kill a burglar or rapist. Or it might kill a fireman, cop, paramedic, pushy salesman, handyman, etc. Even if you don't want some of the previous in your home, you can't shoot them to keep them out, at least not without requesting them to leave and going through a chain of escalation first. Even booby traps that aren't that harmful could cause a lot more damage than expected if somebody very old, very young, disabled, or otherwise more physically vulnerable happens into them. So you can (at least in the US) defend your home yourself with an appropriate amount of force, including lethal force if the situation calls for it. But only because it's you making a reasonable judgement about the appropriateness of the force involved. You can't set a booby trap to harm anyone who goes to the wrong place, regardless of who they are or what their intent is.