My Opinion HA! Accually I wouldn't say a darn thing about the subject. A good idea would be to change the subject instantly, kinda like " Hey.. Isn't Martha from the Photo copy shop sleeping with Joe the mail guy"?!
No serioulsy, when things that upset me, and I find myself in a situation were I KNOW the person is way out and wrong, I let the words go in and out. I try not to let toxic words get to me. Shake it off. She knows nothing. That silly girl.