Using botulinum toxin to treat "anal fissure" or "testicular pain" is technically legal, as doctors have fairly free rein on such "off-label" treaments. But those uses haven't cleared FDA tests the way "severe underarm sweating" treatment has.
So whatever poor sap had to be the first to try injecting Botox into his anus should get some kind of special reward, like never having to stand on the subway. Or, uh, maybe something that doesn't involve sitting, ever. Like a hammock.