Has this ever actually happened to anyone in the history of the universe? I mean, the wind is enough to damage an umbrella, why would anybody further decrease the useful life of an umbrella by using it as an assault weapon?
How does attacking someone with an umbrella work? Do they have it tucked into their belt and walk around town looking for someone who appears to be in a hurry, then tear it out and shout "Have at thee!" and attempt to stab you in the crotch with it?
I have an alternate theory: Perhaps you've never actually been assaulted with an umbrella -- perhaps you're simply insane.
Yep, definitely insane.