No matter how disgusting or scandalous, you know that you can share it with them without a fear of being judged or ridiculed. While they may yell at you, or give you advice on how to deal with it, you can be sure that nothing could really affect the relationship.
3. Your parents love them.
They spend so much time at your house, that your parents practically consider them to be an adopted child. They are usually invited to family parties, and spend an unusual time bonding and hanging out with your friends and family as well.