Put #define true (rand()%1000 != 0) in some obscure C or C++ header file on their system/project. This makes true evaluate to false one in a thousand times, and will make them spend hours trying to figure out why things like infinite loops, aren’t quite infinite.

Other languages should also allow you to do things like this, if not messing with constants, messing with standard library functions.

Our kids swapped the position of our bowls and plates in the cabinets, and our knives, forks, and spoons in the drawers. They definitely won.

Tape over the mouse laser is always a good one

I’ve heard it said that the key to a benign prank is to creates a mixture of momentary alarm and confusion, followed by relief.

A few years ago, I put a sign on my boss’ office door that said that his office was off limits for the week, as the building facilities team was going to be proactively placing humane termite traps in his office for two weeks as a preventative measures to lure any termites in and then release them at a nearby forest. He found it amusing.

True story. This thing happened last week.

Person A: I want to eat something.

Person B: Do you want some of these (B opens a box of boring cookies and shows the contents to A)

A: No!

B: How about these (opens another box of bland cookies)

A: No!

B: (grabs a third box, realizes it’s empty, but opens it carefully not to show anyone what’s inside) Ooh, I’m not showing this to you. (Puts the box away.)

A: I wanna see! (Tries to grab the box)

B: No, it’s mine! (Pushes A further away)

After some futile struggle B let A have the box. A opens it up and realizes it’s empty. We all had a good laugh.

Hide small plastic babies around their house

If they leave their phone unattended take funny selfies and then quickly return their phone to exactly where they left it.

• Short sheet their bed
• If they leave their computer unattended/unlocked:
  • Screenshot it, make that their wallpaper, then hide icons & taskbar
  • (unsure if this still works) Alt + Ctrl + Arrow keys to rotate Windows desktop
• Get a musical birthday card, then hide it (opened) somewhere in their room/office (best under a piece of furniture/couch cushion, etc) so all they can hear is the muffled music
• Remove spring from tip of clicker ballpoint pen (ink cartridge won’t stay out/in)

Replace the eggs in their fridge with convincing fakes that don’t quite seem right.

I saw a video once of a prank where two girls go up to a stranger asking them to take a picture of them across the street. The stranger takes the photo and when the two girls start cross to the other side, a car passes by and the two girls are replaced with two old men wearing the same shirts. Even the Polaroid photo shows the old men. It’s genuinely funny and completely harmless. It just makes the person getting pranked go, “Wait, what the fuck???”

I do hope the people were told that they were pranked though and that they don’t live the rest of their lives thinking they’re insane 😂

ETA: also this video where the guy puts on the collar and leash of his blind husband’s service dog when he asks him to go get his watch. (He immediately reveals himself when the blind husband gets back to pick up his service dog’s leash again and the husband thinks it’s hysterical).

Find a c header file on a program they’re working on.

#define main main

I once hid in a box for, like, an hour so I could leap out of it at my brother.

I made a “spray grenade” to my friend once. Attached a Ty-wrap to a bottle of Febreeze (trigger in) and throw it in his room while he was there. He was pretty quick to seek scissors and cut it but I can imagine it worse without his quick thinking and a worse scent.

Bait t-shirt?

Edit: Bait Airpods then.

Send them a head of white cabbage every week (can use an online grocery service.

If you have access to their dwelling, put all their bedroom furnitures in the living room