A defensive person is someone who takes advice, criticism, and opinions from others in a negative way, they act defensively when they are placed in such situations as to protect themselves and their image from being humiliated, and always try to justify their wrongdoings, besides, they think that everyone is out to get them even their loved ones that only want their well being.
The majority of people are not defensive by nature, they just picked up that bad trait because they were around sick people whom wrongly disapprove their behaviors all the time and question their judgments for the sake of making them feel corrupted and down, call it envy or call it greed. As result, this person confidence diminishes and soon he/she develop the defensive attribute.
Try to get rid of that behavior because not every advice is a bad critique. If a family member or a dear friend is trying to put you on the right direction or give you a piece of friendly advice that does not mean that he/she wants to put you on the spot or embarrass you in front of others or in front of yourself. However, they just want to enlighten you and open your eyes for things you might not see. Frankly, you must differentiate between treating people who love you and people who just do not care about you, realize when you should be defensive and when there is no need to be like that at all.