WARNING!!!!! YOU COULD BREAK YOUR PSP AND YOUR UMD!!!!!! DO NOT TRY THIS WITH ANYONE NEAR YOU!!!! I AM NOT RESPONSIBLE TO WHAT HAPPENS TO YOUR PSP.

I did this with my old psp 1000, it may not work with the others.
Basically, the PSP has pretty good protection for launching discs. If
you release the disc and leave it in the PSP, you can shake the PSP and
the disc won't come out. But, if you hold your PSP at an angle, and
open the disc drive, while giving your PSP a good jolt forward and
sideways while applying pressure to the sides of the system, your disc
will indeed fly out. BUT THIS IS NOT SUGGESTED!!!!