I'm always chewing through mine.
Actually a pipe stem in my mouth keeps me from grinding my molars together as much. What I do is freak out and bite down, just once and they break. It is not from wear - it is from too hard of a bite, after being startled by something.
I have also broken a bicuspid the same way. I was talking when someone touched me wrong and I slammed my jaw shut, but it was crooked from forming vowel sounds, not aligned properly and a tooth broke.
It didn't hurt, but it was sure a bummer!