<human>: Can you provide a brief overview of the text?

A co-worker and I have a feud going and he is stomping me because I am easily startled.  He, however, is not "scareable".  I need some creative ideas to prank him, or something epic to scare him. 
I've done the basics: stole his car keys, put tape over the mouse laser, stole every pen from his office, but nothing satisfies! 

What have you guys done in the past that gets their goats?  

His office is also in the back with the big bosses, so nothing loud or that would get me fired... But feel free to share your own stories!
<bot>: What are some good epic pranks for a co-worker whose not easily scared/suprised, that won't get me fired?