tee:

When I lived in NYC, we were given a self defense class at work that was targeted to protecting yourself on the street against muggers.

High heels and keys were the top choice makeshift weapons recommended for women. Thread the keys through your fingers with the pointed sides palm in and use them to rake the eyes of an attacker. I never walked in heels, but many women did and a good crunch to the top of the foot with a spike heel was a good way to gain a few seconds to run. But most of all we were taught to give a good swift kick to the groin to bring a man down quickly.

To this day, I always thread my keys any time I have to walk at night, especially in dark parking lots.