Co-workers can't resist sweets, especially if they're free? Take plain donuts with no filling and fill them with mayonnaise. Put them in the office kitchen with the sign: "From the Office Management! A Delicacy from Home! Thank you, Tenants!" Then don't stay within spitting distance!
Prankster: Everyone loves a free office snack. That's why I came up with the mayo donut. You need some supplies. You need donuts. You need mayonnaise. You need a Ziploc bag. And you need a knife. What you do is you fill your Ziploc bag with mayonnaise. You're going to push it to the corner and cut a little bit of a hole right there. That makes your donut filler. Then you're going to take a glazed donut. You're going to cut four holes around the edges of the donut. Then, you're going to fill those holes with the mayonnaise. See it looks like your regular cream that would go in a donut. It doesn't taste like that though. So once you have your donut filled, it'll look something like this. Then you place the donuts here. Put up your signs for a Happy Monday, and someone has a delicious breakfast. Not really.
Colleague: Hey! Happy Monday. These donuts will cure the Monday blues. Guys! There's donuts! I love the cream filling. These are the best. These are the best, guys.