Back in my graduate days, I used to bring my lunch to school which consisted of a sandwich and usually a hard boiled egg

Back in my graduate days, I used to bring my lunch to school which consisted
of a sandwich and usually a hard boiled egg. I kept a small jar of salt in
my desk for the eggs. One day I dipped my egg in the salt only to discover
it was sugar. It was easy to spot the prankster(s); everyone in the room was
snickering!

I used to bring my lunches in plastic lined paper bags with bend-over tabs
on the top. The bags were very good and kept my sandwiches fresh. I got
them for free from the pockets of airline seats. One day as I was opening
my "lunch" bag in the lab, the same bunch of pranksters from above gathered
around my table and opened their own barf bag lunches (they had just gotten
back from an out-of-state conference). However, the joke was turned around
on one of them. He was spooning yogurt out of his bag and eating it. After
I told him what it looked like, he lost his appetite.