I go to a school where owning a gun or a knife is highly impractical to say the least.
A gun is obviously the ideal self-defense weapon, however barring that I used to carry a knife on me. Neither of these is an option at my school. This has led me to hit upon a melee weapon that is not only far more dangerous in the hands of an untrained fighter, but one that is more innocuous too: the flail.
Let me explain my construction. It is a green cloth re-usable grocery bag with a large master lock dropped inside and a knot tied in the middle. Simple. Anyone could make something similar with any number of items. However in my opinion, the two I've named are ideal.
Since it is essentially just a bag and a lock, it is highly innocuous even in complete form, but when separated into it's components can go literally anywhere, even places where less dangerous knives are banned. In fact, it has far less potential for legal trouble, across the board, than a gun or knife.
Some may dispute that a flail, like I've described, is more dangerous than a knife. They would argue that a knife offers rapid lethality in the hands of a skilled fighter. This is true, but I for one, am not exceptionally confident in my knife fighting skills, and I doubt the majority of people interested in a self-defense weapon are.
A flail is easy to use. You swing it hard, at your assailants head, and they will go down, no matter if they are exceptionally strong, and even if you aren't the most athletic person. Even a body or extremity shot from an object traveling so quickly is likely to be devastating, if not completely incapacitating. Moreover, the blunt force trauma of the flail is certainly more disabling, which is of utmost importance in a tight situation.
I could go on and on about the advantage of a flail, or similar impact weapon, over a similarly sized edge weapon. Thoughts, sherdoggers?