A person who always takes and never gives, especially in a self-centered or exploitative manner, is often referred to as a "taker" or a "moocher." They are someone who consistently benefits from others without reciprocating or showing consideration for the needs or interests of others.
Other terms that might describe such a person include "freeloader," "user," "leech," or "selfish opportunist." These terms generally imply that the individual takes advantage of others' kindness or resources without offering anything in return or showing appreciation.