A half-full stainless steel hydro flask with a nylon lanyard. Functional and discreet.
My friends and I spent an evening discussing what you could use for self-defense in a vehicle that wouldn’t be illegal. A double-sided dildo came up, for the shock factor. Imagine getting carjacked and slapping them with that!
For home defense, metal spoons and titanium straws can be surprisingly effective. Frying pans too, especially cast iron. Even a dog’s heavy tug-of-war rope could do some damage!
A tightly rolled-up magazine can be great for close quarters. Also, a thick belt can be handy as a whip or to block attacks.