I’ve been thinking about that myself. My best guesses are 1) that the resulting hollow would be a great breeding ground for anaerobic bacteria and/or other parasites, and/or 2) since the procedure was purely cosmetic his insurance (probably Medicaid) wouldn’t cover it. Just guesses, mind you.
If it were me, I would get a prothetic skull made and then have fun with it. You could:
1. Put a little trap door in the side and randomly pull things out while talking to someone, like little birds or loose change.
2. Make a prothetic that looks like an exposed brain. I would also make it throb. Then go into a pharmacy and ask for the aisle where they have something for a bad headache.
3. Instead of a fake exposed brain, it could look like a bunch of circuits. Then ride around on buses and tell people you are a robot from the future.
4. You could have a real arrow go through the prosthetic. When people tell you to stop fooling around with that old gag, you could pull out the real arrow and watch women faint.