Be subtle. Don’t overdo it. Instead of screaming swear words at people and claiming to be “seeing” things, maybe talk in a low whisper and look at “someone” next to you who isn’t there.
Repeat yourself. Pretend you did not. Insist you did not.
Take a sip of soda, hum while you do it, and insist it isn’t you.
But be warned:
Be ready to reveal the joke. In most states, crazy for real can cause an immediate and sometimes permanent removal of your most basic rights and can land you in a mental ward.
I used to volunteer at a mental hospital, teaching adults how to read. The only thing I had to watch out for was their unpredictability. We’d be reading a book one minute, when all of a sudden they’d do something, like taking a nap; put their head down and start snoring, and REALLY be asleep. Maybe I bored them.