Evil.

[Reginald Ret]

It's amazingly easy to make yourself sick without actually endangering your life.
On the first day you take plenty of laxatives and try to do your job as good as possible.
You will spend a lot of time on the toilet but your go-getting attitude will convince the boss that you really want to work.
If the boss doesn't tell you to go home start sneaking laxatives into the company coffee/watercooler/donuts so the 'disease' spreads.
If that gives no result in 3 days try to put laxatives in your boss's foodstuffs.