If you normally wear glasses, wear contacts.
The other night, I went to the Jagermeister Music Tour's kickoff show at the Electric Factory in Philadelphia. Unfortunately, I wasn't prepared for the opening act, the Wolfpac. Their set involved four scantily-clad dancers on stage (they were wearing schoolgirl uniforms, at least for the first 2 or 3 minutes), half-audible rap (their mics kept cutting off), and a mosh pit.
For some reason, they also had a trampoline onstage. One of their crew then jumped onto the trampoline, and jumped out about 6 or 7 feet, right into the front rows of the crowd.
Where I was.
This left the right ear-thing of the frames extremely bent out-of-place. Attempts to correct this bending resulted in the piece snapping off at the joint.
I managed to continue watching the concert, the glasses managed to stay on with one ear-thing. Then, during Systematic's set, the mosh pit a row or two behind me (I rightfully gained my spot at the front row) got ugly. I was hit from behind. Glasses flew off. Panic.
Fortunately, the glasses landed in my hat, which landed in front of the guardrail. Security gave them back to me, along with a piece of gaffers tape so I could temporarily repair my glasses.
The next day, to the optometrist's, for new $135 Polo titanium frames. A costly mistake indeed.