When I was younger, I used to climb on things a lot. Monkey bars, large speakers at bar/bat mitzvahs/weddings/big parties, stairs, roofs, etc. I'm guessing that's how my first nickname came to be. My dad thus named me "Monkey". I also had a white stuffed monkey that I carried around with me a lot. So I guess that could have been a contributing factor.
My older brother and I attended the same elementary school at the same time (which later switched, with my younger brother and I attending at the same time). My older brother had a teacher who had the same name as the principal, which confused people a lot. I used to go to his classroom during recess (our class and his class had different recess times since I was in first grade and he was in fifth) and interrupt his class and tell his teacher on things that he had done at home. I guess I was a real riot, because when I had the same teacher for fifth grade a few years later, she used to regale the class with tales of what I had said. "Mrs. B! Do you know what my brother did last night?!?" I'd apparently say, wagging my butt from side to side like most children do when they tease. "He got in sooo much trouble!" I'd make his class laugh with all the things he did, while his face would turn red. When she'd tell us the stories of what I used to do, it would make MY face turn red, so I guess I got what was coming to me. Sort of. Anyway, because I hadn't really changed much in size since first grade (I was quite the shorty), Mrs. B would call me "Squirt". Then one day she decided to change my nickname to "Midget" (which was not as traumatizing as some nicknames for other children). One day she got confused about which name was mine for that day, so when I was called early to go home, she said "Hey Squirt! No...Midget! No...Squidget!" and from that day on in fifth grade, Squidget stuck. All of my friends called me Squidget from then on... or rather, until about seventh grade.
In seventh grade, I changed from being a camper at my summer camp to being an L.I.T. or a "Leader in Training". This was one step down from Counselor in Training which was a step down from Counselor. Well, when I started, my group decided that we wanted to have Camp Names, just like the CITs and Counselors! Of course, this theory was kind of pointless since everyone knew our names anyway, but we stuck by the idea and picked camp names. Most people chose names like "Sunshine" or "Cupcake" or "Curly", but I went with "Piglet". Piglet was my favorite character from Winnie the Pooh (still is!), so I decided Piglet would be a good choice for me. He was short and cute and pink and I thought, "Perfect! I'm short and cute and I have red hair, so we're virtually the same!" Sweet. So my nickname from seventh grade until my sophomore year was Piglet. I kind of regretted picking that name later, since it sort of associated me with being fat (which I'm not, really), but I dealt with it by sticking by my decision that Piglet and I are similar...in that we're short and cute and shades of red.
My sophomore year in high school a lot of my friends began taking Spanish, and decided to nickname me "Estar, the spanish verb meaning to be", which was then shortened to "Estar" or just "to be". Not much of a story there. Go Spanish.
My freshman year in college, our RA Kristie decided to give all of the girls on my floor nicknames by using the first letter of the name and adding and "o" to it, then doubling it (for instance, Paula was "Popo", Rachel was "Roro", etc). However, my name starts with an E, which makes it kind of difficult for it to follow the same model. So she was going to use the second letter of my name, S, but there was a girl with an S name a few doors down. What a pickle. So she decided to use "ThoTho" as my name. Which sounded like anyone who tried to say my name had a lisp. That nickname stuck for about five minutes. Sweet.
My sophomore year I was in with a new group of friends, who nicknamed me "Sta". We had been watching The Office and decided to give each other nicknames, and since "Big Tuna" was taken, I got Sta. A few weeks later, that same group of friends changed my nickname to Oyster. They thought it was clever because I'm Jewish (so, "Oy") and the rest of my name... (hence the "ster"). And that's who I've been ever since.
So much for a stable identity, eh?