Dork is really something of a harmless insult. In most cases, "dork" is better than "stupid".
Of course, it would also depend on how that word is used. If it was from a friend to a friend, it's not to be taken offensively. If it's from a person who is always figuratively speaking, it's also not to be taken seriously. If it's from a person who's really mean, then it's likely that it is like saying "stupid". We use it here from time to time and it's usually for a chuckle. So... don't be a dork! 
