Just found the perfect argument concerning umbrellas, so i'm gonna to link it here.
It is one of the older entries in John Walker's blog, which I discovered by accident.
"The moment the tiniest droplet of rain is titrated from a cloud, up swoosh these ridiculously huge, and hugely dangerous weapons, endangering anyone who has managed the self-awareness to recognise that they are waterproof. Dodging the genuinely harmful metal spikes that begin spinning down all sides of the streets is like something from a Tomb Raider game, except without the medpacks and calming slaughter of endangered species. If someone were weilding anything else of that size and lethality, they would be immediately arrested."