You're so kind that it's hard for you to believe that other people aren't, too. People could mistake your caution and need for security as weakness and take advantage of you.
If there's someone who's always rude to you, claiming your ideas as their own, or taking you for granted, there are two things you can do. One is nothing. Do nothing and the situation won't change, but you'll have to be content with the status quo.
The other is to teach the person how you want to be treated. If you dislike the way a friend makes fun of you, even in jokingly, speak up. The friend will listen and change the behavior - or not. You can then decide if that's a friend you want to keep.