I once used my keys in a fight, before I knew any martial arts, on the way back to my bedsit in Oxford. Some guy tried to grope me in the street, so I punched my front door key in his eye, with a big and nasty yell. I have never seen a man run so fast.
I promptly got told off by my ex, who had been wandering ahead with his mates. Apparently I should have screamed girly fashion and waited for the cavalry to arrive.
Way to go, Mary! nothing quite like some unexpected counter-violence to scare off your basic badguy