I'll start.
Wait until you know his supperiors will be in, and then mail a super strong smelling bag of weed or perhaps a more serious drug-- to the company in his name. If we are assuming the person executing this is an employee, they will be in a perfect possition to discover it, and deliver to management.
Requires good mail timing. Small flaw in that management can drug test.
Anyone else have some creative and practical ideas on how someone might get their boss fired?
I got my boss fired a few months ago. The imbecile made the mistake of breaching privacy regulations with an employment agency. A few calls to the right authorities and the bitch was immediately terminated. So was the recruitment agent.
Getting someone fired is a lot easier if they're incompetent and foolish enough to commit crimes in view of the entire staff.
Record audio on your phone whenever you are around him. Then create a collection of the worst recordings, and send them anonymously to his superiors.
This assumes your boss does something worthy of getting himself fired or transferred, and that he is not valuable enough where he is to move or get rid of. If he's valuable and generally abides by the rules, good luck on getting rid of him. Companies will smooth over misconduct if replacement means considerable money loss.