You can list whatever you feel describes your employment situation. If you are disabled, you could put disabled as your occupation, or unemployed. The occupation you enter does not affect your tax return.
Put unemployed if you like. The IRS could care less what your occupation is, so long as you pay your taxes. Here's some examples of what I've actually seen in that field on returns in the past.
Occupation Real Job
Mass Murderer Pest Exterminator
Serial Killer Same as above
Human Trafficker Modeling Agent
Drug Dealer Pharmacy Technician
Car Jacker Worked for an automobile repossession company
Hijacker Aircraft Reposessor
Money Launderer This guy worked at the U.S. Mint. His job was to wash newly minted coins.
Terrorist Eradicator Navy Seal (I'm guessing he was on seal team six - but they won't say)
Computer Hacker Works for the CIA – nuff said.