What should I do if my friend is mad at me because I like the same boy as her?

This is when you can pull the "I saw him first" rule. If your friend liked the boy before you and told you before you started to ike them, then you should respect that. When you start to say that you like them too, after they told you that they did, it makes her feel like you didn't listen. If you liked him first and told her, then she reallly has no right to be mad. If anyone should be mad, it would probably be you. Just talk it out and explain that you feel disrespected because you trusted her and she then said she liked him too. If she stays mad, she isn't a really good friend. If she understands, then she is a good friend.