A short disclaimer: I acknowledge that "introvert" and "extrovert" are basically arbitrary categories that try to fit people into boxes that they don't necessarily fit into. For example, I would categorize myself as an "outgoing introvert" because I think it is important to meet new people and I enjoy being social, it just usually takes a lot of effort to get to know someone and I often feel tired afterward. Below are some characteristics typically associated with the introverted category. Individual people may experience some, all, or none of them.
1. You get tired of people telling you you need to be more extroverted
Sometimes it feels like everyone is trying to turn you into an extrovert, especially when they tell you that you should "loosen up" and "just have fun" or that talking to people "isn't such a big deal."
2. It's not that you don't like to do things, you just don't always want to do them with other people
Sometimes, you just want to be alone, but you don't want to cloister yourself in your room. You wish that it was more socially acceptable to do things alone because you feel like everyone is watching and judging you if go out in public by yourself (even though they probably aren't, it still feels like they are).
3. Small talk is annoying
Sometimes people say whatever comes into their mind... however inane. No, I don't need a step-by-step rundown of everything you did today.
4. Communication can be hard
It's hard to just come out and say what you want, especially when it involves emotions. You feel vulnerable expressing yourself and only do so to your closest friends. But sometimes you expect other people to be able to pick up on your on non-verbal cues but they just don't get it.
5. You are perfectly happy if your plans get cancelled (most of the time)
Watching a movie or reading a book instead of going out is perfectly fine with you. You are often relieved when plans are cancelled because it means you won't have to make an effort not to be socially awkward.
6. Sometimes your thoughts carry you to dark places
Sometimes you end up hardcore daydreaming and thinking some really deep thoughts. And then you realize why other people make small talk and talk about unimportant things-- life can be really depressing if you think about it too hard.
7. Sometimes its ok not to talk
You can't stand people who feel the need to fill every silence with meaningless babble. Its nice to sit in silence with someone who understands.
8. Your best friends are the best
Contrary to what some extroverts think, you do like people. You just don't like meeting new people because you'd rather avoid the initial awkward phase and skip right to the deep friendship phase. When you do connect with someone, it is very special.
9. Best friends make everything easier
It feels ok to go to a party with a bunch of people you don't know as long as you have someone you know with you. Just don't let them leave...