Besides, why do friends tease you?
Just remember that when your friends tease you is most probably because you give them a reaction. You might be getting angry or might be crying in front of them. This is the main reason why people tease you.
Similarly, is teasing a good sign? "Teasing is meant to be lighthearted and playful, whereas negging is specifically meant to put someone down so they'll be thrown off guard – and then become interested in you." So as long as you're keeping things light, teasing your crush is perfectly normal, and doesn't mean you'll blow your chances with them.
Accordingly, why do people tease?
Some people use teasing as a playful way to feel closer to another person or to show friendship. In other words, they only tease the people they are comfortable with and generally tease about things that are shared between them like a little-known quirk or action.
Why am I the friend that gets made fun of?
Every person who has ever made fun of you was doing it because they aren't happy with themselves. They are hurting inside, and don't feel like they are good enough. So, they try to take out their anger on you, or try to do it to make people laugh to feel like someone accepts them.