Is it a sign of insecurity/immature when a boyfriend calls you names?

Does he call everyone else Dork, or just you? If he uses it all the time, then it's probably a habit, albeit, a bad one. It also depends on his age, if he's pretty young, it could be that he likes you and doesn't really know how to express it due to his immaturity around girls. He may be using it to mask his true feelings for you. Or, he is just a jerk, and you need to straighten him out right now before you waste too much time on him. Either way, you should never let anyone call you names, so set him straight about what treatment you will except and what you won't.