Oh, let's see...
I liked hiding in small places, especially if it was a strange place for a person to be.
I was obsessed with secret doors and rooms. Always looking for them in every family member's house, and every house I lived in. The closest two were my first house in california, where the hall closet was my nana's bedroom closet on the other side (and only I could squeeze through those boxes)...and an access to under the house from the garage in a much later house up here. I *really* wanted something better than the guided tour at the winchester house. >_>
I did pretend to be a dog sometimes. My parents would say, "Ok, no dogs at the dinner table, you have to act *normal* now".
I've always loved off-the-wall semi-relevant riddles. Jokes, based on a word based on a topic of interest, but with references thrice removed from context. I've known a few people who could keep up with those, that's always a tingly sensation.
Spinning in office chairs as fast as possible. For HOURS if not interrupted. The sideways pull on the inside of my head...the rush of speed even though it was just a chair...and the world around me becoming a meaningless blur. A wonderful distraction.
Inside forts, yes, definitely. Including couch forts, in the living room, at 2 in the morning when everyone was asleep. The nightmares couldn't get me out there. It was peaceful. And mischievous fun!
Trying to imitate the traps from Home Alone and Shipwrecked. This got me banned from watching those movies and thank goodness no one was hurt!
Pretending to be Battletoads with my best friend, with plastic baseball bats as the alien legbones. Beating up pillows.
Stacking couch cusions and pillows, climbing on top of the tower, teetering back and forth and making computer noises, as my "time machine to Endor".
Trying to convince myself that I was:
-A robot
-An alien
-A werewolf/vampire/elf
-From the future
As a self-diagnoses of my wierdness and a distraction during school. Taken to the extent of trying to convince classmates, i.e. sticking wires from an electronics kit from my wrist, into my shirt, out the collar and around to behind my ear. Or making statements about reality that sounded incredible but possibly feasable, at least to children my age.
Mimicking television and videogame characters. Coming up with backstory for how I got to this world and what I was doing pretending to be this normal kid.
Staying in the bath long after the water was cold, just to play with the texture of shriveled fingertips. Did the same with the texture on leaking balloons, or releasing air from a balloon while touching the surface.
And that's all I can think of at the moment.