I'm really not big into playing "mindgames" or trying to "trick" my fellow gamers somehow, but I happened upon a sort of funny situation, and well, the GM and I kind of ran with it.
Here's how it all started. The party found a magic ring of some sort, and we all went for it. "Mine!" Well, I think the GM kind of ran with the idea that it was a ring that we all sort of "wanted" and he made it kind of like the Ring of Power from LOTR. You desire the ring. You want to have it. It has that same sort of weird influence on people.
Anyways, my character wound up with the ring.
As we camped, I decided to play it off, so my character went away from the party to admire his "precious." But I didn't announce what I was doing, I just said "I step away from the rest of the party for a while"
For some reason, this aroused immediate suspicion! The other party members automatically assumed I was up to something, though I can't fathom what (maybe sneaking back around and stealing from them?) To their credit, my character is a rogue.
Anyways, I do this a few more times when we camp (announcing that I had to answer nature's call or some other such excuse), each time with the same suspicious response. Interestingly enough, no one tried to check on my character or go find out what he was doing...
By that point I was having fun with this, so on the third time I wrote a note to my GM.
I said, "Oh yeah, while I'm away." and handed him the note.
On the note I simply wrote "Nothing."
Now, one of the other players states that he was checking his possessions to make sure he still had all of his belongings.
The GM asked him for his character sheet.
The Gm took the character sheet, looked it over, and said "Oh yeah, there's that."
He took a pencil and rubbed the eraser on the sheet, then handed the sheet back.
The player went "Oh great!"
he looked over his character sheet up and down, and tried to figure out what was missing.
"Just what did you erase??" he asked.
"Well, I can tell you that what I erased on that sheet was the same thing that he [talking about me] wrote on that note."
Which, of course, is nothing.
We'll see how long this lasts.