Bullying: everyone does it.

At a very young age I was a victim to bullying, but as a got older I saw myself becoming not only an enabler to bullying, but a bully myself.

First let me tell you a few stories (short..I promise):
When I was little I was unfortunate enough to have my fathers teeth...(nine years of orthodontists, after story), I was always different then my schoolmates, always striving to fit in.
I was in class drawing a picture of something, suddenly I felt a pull on my hair. A girl named Jessica threw something on my picture...what was it? It was my hair, she had scissors in her hand and laughed at me.
After a few more sad episodes at that school I was in elementary school, when a girl pulled me aside and told me how badly I needed a makeover, apparently all the boys thought so to. All I wanted to do was read my book(which was about the solar system, not homework).
Then high school...where do I start? Freshman year I bought these really cool Jean shorts that looked like something Christina Aguilera wore. I was in the bathroom stall when two bitchy girls came in (well aware that I was in there) made fun of my new Jean shorts, making me cry. I ran out quickly as they laughed, running to my friends. I took back those jeans that night.

I'm pretty sure there have been more times, I just can't remember. Along with those sad stories, I witnessed bullying and didn't stop it, until high school at least. I knew better then.
But just recently I did some mean things, mostly I was either hurt or just being bitch(which is very much not who I am.
I lost a friendship recently,which put me in a depression and I finally got over it(at least that's what I told people). She broke my heart, so I talked shit about her, cussing her out anonymously on formspring.com.
Next I posted some mean things about another girl on another site, doing this for the approval of a friend (trying to fit in, basically).

I do feel bad, I can't take back what I wrote. But I'm sorry.
A few years ago, I got anonymous messages telling me to kill myself. Telling me I was ugly,fat,etc..
I would never listen to these messages and would never write them.
My question...what if I did listen to them? Would they feel guilty?