I've been doing things to get my jawline more defined for years. Other then chewing high resistance things like jerky or Triscut snack crackers, I wouldn't know...LOL...but other than that, getting braces seemed to buff my jaw up. As always you would be able to see your jaw better if you had less fat in your cheeks, I have quite a bit. I also punch myself in the jaw from time to time, just to let it know who's boss.
And yes, I do really do these things.