I have a very dear friend who I think of as my little sister. When I've been introduced to prospective young men, I get them aside and tell them simple "look, you don't have to be afraid of me- I only swat flies, kill them cleanly. She isn't as nice as I am when she's angry." (Keep in mind, my public face can be very scary, and I usually ramp it up to the King Kong class when I give that piece of advice.)