As a compulsive flosser, I don't spray food particles all over when I'm flossing. Would you feel the same way if she were using a toothpick? While she might have put it back in her pocket, I have flossed on a plane before. I don't sit there with my mouth wide open spraying people with my spit or food, but I also don't have a problem flossing. People comb their hair, pick their nose, cough/sneeze without covering their mouths, hack from a smoker's cough, wear too much perfume, remove their shoes (and socks), flatulate, take up too much time in the bathroom, spit out food onto their plates, wet their diapers, etc.

How do I know? Because I have sat next to individuals that did one or more of the things above.

Coughing on someone is disgusting. Sitting next to someone with a wet diaper is also not enjoyable. And while plenty of people have talked about the toenail/fingernail clippers, I have not experienced that yet.