Dentist: *severe lecture on the importance of flossing, you absolutely have to, if you don't floss your teeth will definitely all fall out, etc*
Me: The thing is that I hurt myself when I try? My teeth are too close together for the floss to fit between them. I guess it's because my wisdom teeth pushed the others forward. If I try to force it, I just end up bleeding.
Dentist: Oh. Me, too, actually! - Yeah, you don't want to try and force it, you'll just get a gum infection. I don't actually do it.
(I have never in fact had a cavity.)