On a previous job, my coworkers were jealous because I started going out for lunch some days of the week instead of staying with them at the office kitchen. So every time I went out, I came back to find some kind of small prank, and also a sign reading "Lunch Break Maffia Attacks Again". Once they made garlands by glueing/taping together a lot of sauce packets (mayonnaise, ketchup, and so on) in different patterns and decorated my whole box with them.