I'm not a huge prankster, to be completely honest, and when I do prank I'm usually laughing to hard to remember to photograph it. I went through my "LOL" folder, though, and found a few highlights which go well back in time, all of them around fun times and prankish like things, so I thought I'd share for Strawberry's Prank Meme (honestly, I'm a little jealous she gets pranked as much as she does - it's kinda sweet; her reactions make it worthwhile, of course).
Early days on Second Life I had a friend who bought a Homestead island for a year and let us all play on it. We all set our homes there, rezzed all sorts of nonsense, and occasionally played pranks. This one was started by Bash Quandry, one of the few cousins I've met on Second Life; he built the bullboard so that we could see it from everywhere on the island. I added the picture of his butt which he had sent to us all no-transfer, and posed myself using some free poses. This was early on in photographe, too, and you can see my shiny freebie clothing as well.
One time when I was clearing old landmarks, I found a whale. I also got kicked out of a few places (and later questioned as to why I was there by someone who was not pleased his home had been a store once), but I'm still glad for all of that because i found this amazing whale falling through the sky endlessly over Second Life, with a small bowl of flowers nearby. I was enormously fond of it, and while it's not a prank per se, let's call it an inside joke hidden on the grid.
One of the games I would sometimes play with my friends is building a giant ball pit, decorated with the best in rainbow balls of course, with all of them set to physical. The giant, physical ball is actually my favorite prank for afk people; I have moved people-in-balls all kinds of places, giggling the whole time, and usually they enjoy it too when they get back. I'll have to remember to take pictures next time we take someone afk for a walk in a giant ball - it's rather like being a hampster, really.
I also sometimes decorate people, or build them cages. Bear went afk once for hours, and I ended up building a Bear Cage for him. Sadly, I think he logged before he ever saw it. Sadface, sadface. Now... I need to go read everyone else's posts to see what I should be doing in Second Life. Muahahahahahahahhaha.
( More pictures here. )