It seems like your nemesis has some flaws to be exploited. Is he OCD? What is the work environment like? A cube farm? Private office? Something else?

Start by spreading the love. Crack open a can of tuna ever so slightly. Hide it deep within his desk or cube farm environs.

A friend once told me about the "milk bomb" prank where you fill an airtight glass jar with sour milk, insert a chicken or turkey leg into the liquid, then screw the lid on.  Hide the jar in the victim's car on a hot summer day and the thing eventually explodes, practically ruining their car with the stench.  Ah, here's a how-to online, of course. 

http://www.urbandictionary.com/define.php?term=milk+chicken+bomb