It sounds like you are a student and a good friend.  I'm not sure if your school has an ethical code that teachers must adhere to, and I don't know if it would find fault with the teacher making this comment.  I think the comment is unacceptable, but legally I don't know what you can do.

However, I do think there are some steps you can take to ensure it won't happen again.  I would report it to the school's administration, today if possible.  Get it on the record.  If you can get your friend or other students form the class to go with you even better.  Just remember it will probably come down to your word against the teacher's.  So if someone heard from someone else the teacher said that, that isn't good enough.  When speaking to the administration, stay calm and state the facts.  Then ask them what they plan to do about it.  Now, keep in mind, there actions might not be what you want them to be.  

If you feel you aren't getting anywhere, tell your parent.  They might be able to follow up with a phone call or email.

Another ideas is to tell another trusted teacher in the school what happened.  They might be able to give you some support in reporting the matter.

Standing up for you friend is a good thing.  What the teacher said was wrong and very unprofessional.  If it happens again, keep reporting it.  Good luck!