Cancer Patient Beg-Off
Have someone shave all the hair on their head, but make sure to do it badly. Intentionally miss patches of hair on the eyebrows and head, and make sure to try to get some razorburn for that obviously-just-shaved look. You could also use an electric hair trimmer to leave a little bit of hair and make it even more obvious. Leave the hair on your arms or wherever else as if you forgot to shave it. The point is to be completely unconvincing.
Then hit the streets and beg for money and see how pissed people get when they think you're scamming them. You could walk around asking for money, or even chase after people to show that you're actually fit but when they question whether you're sick or not, you could do an unconvincing couple of coughs as if you suddenly realized you're not acting well enough. You could even sit next to a beggar to see who gets the most money, or if people give the beggar money just to spite you.
Hopefully they'll calm down enough to sign the release after you give the money back and explain the joke!