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.

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

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

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.

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.

Bait t-shirt?

Edit: Bait Airpods then.

Tape over the mouse laser is always a good one

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

Detonate a nuclear bomb

Piss in pizza box, freeze it, then leave it in front of someone’s door if they’re throwing loud parties.

Liquid @ss is astonishingly effective, can get it cheap on Amazon

Buy something that makes noise periodically, hide it. They’ll go nuts trying to find it.

Record satanic rituals on a voice recorder. Tie string around it, open window quietly, lower voice recorder to hover above downstairs neighbor window. Set it to play. Can freak religious people out.

• 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)

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

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.

Just don’t. Pranks are a form of bullying.

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.